Sleep: The Complete Guide

Key numbers at a glance

How sleep works

Sleep is not simply the brain switching off. Through the night you move through repeating cycles of lighter sleep, deep slow-wave sleep and rapid eye movement (REM) sleep, each lasting roughly 90 minutes. Deep sleep tends to dominate the first half of the night and REM sleep the second half, which is why a shortened night, or one broken in the early morning hours, does not cost you a little of everything equally. Brief awakenings between cycles are normal; most people never remember them.

Two separate systems decide when you feel sleepy. Understanding them explains most sleep advice, including the parts that seem counterintuitive, such as getting out of bed when you cannot sleep or keeping the same wake time after a bad night. When the two systems line up, sleep comes easily. When they pull in different directions, as they do after a long nap, a late coffee, a night shift or a flight across time zones, you can be exhausted and still unable to sleep.

Sleep pressure

From the moment you wake, a chemical signal called adenosine builds up in the brain. The longer you are awake, the stronger the pull toward sleep becomes, and sleep clears it again. Caffeine works by blocking the receptors adenosine acts on, which is why it masks sleepiness without repaying any of the debt. Naps release some of the pressure, so a long or late nap leaves less of it to carry you to sleep at bedtime.

The body clock

Alongside sleep pressure runs a roughly 24-hour internal rhythm, the circadian clock, which sets when you feel alert and when you feel drowsy regardless of how long you have been awake. Light is its strongest signal, especially morning light, and the hormone melatonin rises as darkness falls. Outdoor daylight, even on an overcast day, is many times brighter than ordinary indoor lighting, which is why getting outside soon after waking is one of the most effective and least used sleep tools there is.

How much sleep you need

The CDC and the American Academy of Sleep Medicine advise that adults get 7 or more hours of sleep a night on a regular basis. That is a figure for sleep, not time in bed; most people need to allow a little longer than their target to achieve it. Needs vary somewhat between individuals, but very few adults function well over the long term on less than 7 hours, and many people who believe they have adapted to short sleep perform worse on testing than they realize.

Children and teenagers need considerably more, and the ranges below include naps for the younger age groups. Teens are a particular concern: their body clocks shift later during adolescence, so they feel sleepy later at night while school schedules still demand early starts. The American Academy of Pediatrics has recommended that middle and high schools start at 8:30 a.m. or later for this reason.

A useful self-check is how you feel during the day rather than how many hours you log. If you wake unrefreshed, need caffeine to function, or fall asleep easily in meetings, while reading or as a passenger, you are either not getting enough sleep or not getting good enough sleep, and both are worth addressing. Keep in mind that sleepiness and fatigue are different: sleepiness means struggling to stay awake, while fatigue means feeling drained or lacking energy. Fatigue with enough sleep can have other causes, such as anemia, thyroid problems, diabetes or depression, which a doctor can check for.

• Infants 4-12 months: 12-16 hours including naps
• Toddlers 1-2 years: 11-14 hours including naps
• Children 3-5 years: 10-13 hours including naps
• Children 6-12 years: 9-12 hours
• Teens 13-18 years: 8-10 hours
• Adults 18-60 years: 7 or more hours
• Adults 61-64 years: 7-9 hours
• Adults 65 and older: 7-8 hours

Why sleep matters for your health

Regularly sleeping less than you need is linked to a higher risk of several long-term conditions, including high blood pressure, heart disease, obesity and type 2 diabetes. Sleep affects the hormones that regulate appetite, so short sleep tends to make you hungrier, particularly for energy-dense foods. It is also linked to weaker immune defenses. These are associations from large studies rather than proof that every short night causes harm, but the pattern is consistent, and sleep is one of the more changeable risk factors you have.

The effects on the mind are quicker to notice. A few nights of poor sleep reduce attention, memory, judgment and emotional control. Sleep problems and mental health conditions such as depression and anxiety feed each other: each makes the other more likely and harder to shift. Treating a sleep problem can make other treatment work better, which is a good reason not to accept poor sleep as just part of being stressed.

Then there is safety. Drowsy driving causes serious and fatal crashes, and sleepiness impairs reaction time in ways people consistently underestimate. Warning signs include yawning repeatedly, drifting from your lane, missing an exit or not remembering the last few miles. Turning up the radio or opening a window does not fix it. If you notice these signs, pull over somewhere safe and rest, or let someone else drive.

What gets in the way of good sleep

Caffeine is the most common culprit that people overlook. The FDA cites 400 mg a day as an amount not generally linked to harm in healthy adults, and an 8 fl oz (240 ml) cup of brewed coffee contains roughly 80-100 mg. But caffeine stays active for several hours, and how long varies widely between people, so an afternoon coffee can still be working at bedtime. Falling asleep easily does not prove it has no effect; caffeine can make sleep lighter without delaying it. In pregnancy, ACOG advises keeping caffeine below 200 mg a day.

Alcohol makes many people drowsy, which is why it is often used as a sleep aid, but it fragments the second half of the night and suppresses REM sleep. Large evening meals, nicotine, and vigorous exercise very close to bedtime can also delay sleep for some people, although regular exercise earlier in the day generally helps. Bright light in the evening, from overhead lights as much as from screens, pushes the body clock later.

Many problems that disrupt sleep are medical: pain, heartburn, needing to urinate at night, breathing problems, hot flashes around menopause, an overactive thyroid, depression and anxiety. Some medicines, including certain decongestants, steroids and some antidepressants, can affect sleep too. If a sleep problem started around the time a medicine was started or changed, mention it to your doctor or pharmacist rather than stopping the medicine yourself.

Insomnia

Insomnia means persistent difficulty falling asleep, staying asleep or waking too early, despite having the opportunity to sleep, with effects on how you feel or function during the day. Short episodes after stress, illness or travel are common and usually settle. When it happens on 3 or more nights a week for 3 months or more, it is classed as chronic insomnia. At that point it often keeps itself going: worry about sleep, extra time in bed and irregular schedules become the problem even after the original trigger has gone.

Guidelines recommend cognitive behavioral therapy for insomnia (CBT-I) as the first-line treatment for chronic insomnia, ahead of sleep medicine. It is a structured program, usually over several weeks, delivered by a trained clinician, in a group, or through digital programs. Its benefits tend to last after treatment ends, which is not true of sleeping pills. Many people with insomnia have never been offered it, so it is worth asking for by name.

Sleep restriction can make you sleepier at first, and it is not suitable for everyone without supervision. If you have epilepsy, bipolar disorder, a job where sleepiness is dangerous, or severe daytime sleepiness, talk to your doctor before trying it. General sleep hygiene advice on its own is less effective than full CBT-I for established insomnia, so do not be discouraged if tidying up your bedroom habits has not been enough.

• Stimulus control: go to bed only when sleepy, and if you have been awake about 20 minutes, get up and do something quiet in dim light until sleepy again
• A fixed wake time, 7 days a week, regardless of how the night went
• Sleep restriction: temporarily limiting time in bed to roughly the time you actually sleep, then extending it as sleep consolidates
• Cognitive work on the beliefs and worries about sleep that keep you alert at night
• Relaxation techniques and a consistent wind-down period

Sleep apnea

Obstructive sleep apnea happens when the upper airway repeatedly narrows or closes during sleep. Each time breathing stops for 10 seconds or more, or becomes very shallow, the brain briefly rouses you to reopen the airway. You rarely remember these awakenings, but they can happen many times an hour and leave sleep badly fragmented. The classic signs are loud snoring, pauses in breathing or gasping that a bed partner notices, and daytime sleepiness. Morning headaches, a dry mouth, waking to urinate and trouble concentrating are also common.

Sleep apnea matters well beyond tiredness. It is strongly linked to high blood pressure, atrial fibrillation, stroke and drowsy-driving crashes, and many people who have it have never been diagnosed. Risk rises with excess weight, a large neck, older age, male sex, menopause, alcohol, and features such as a small jaw or large tonsils, but it also occurs in people of normal weight and in children.

Diagnosis is by a sleep study, which is now often done at home with a small recording device. The standard treatment for moderate to severe apnea is CPAP, which delivers air through a mask to hold the airway open. The first couple of weeks can be uncomfortable; mask fitting, humidification and pressure adjustments often solve the early problems, so contact your equipment supplier or sleep team rather than giving up. Other options include custom oral appliances, positional therapy, treating nasal blockage, weight loss and, for some people, surgery or an implanted nerve stimulator.

Other sleep disorders worth knowing about

Restless legs syndrome causes an uncomfortable urge to move the legs, usually in the evening or at night, that eases with movement. It can run in families and is sometimes linked to low iron, pregnancy, kidney disease or certain medicines, so blood tests are often part of the assessment. Narcolepsy causes overwhelming daytime sleepiness and, in some people, sudden muscle weakness triggered by strong emotions such as laughter, called cataplexy. Both are under-recognized and treatable.

Circadian rhythm sleep disorders occur when your body clock is out of step with the schedule you need to keep. The most common is delayed sleep phase, especially in teens and young adults, in which a person cannot fall asleep until very late and struggles to wake for work or school. It is not laziness, and carefully timed light exposure and schedule changes can help. Parasomnias, such as sleepwalking, night terrors and acting out dreams, are more often seen in children; new dream-enacting behavior in an adult should be checked by a doctor.

These conditions are easy to mistake for ordinary poor sleep, stress or a busy life, which is why they often go undiagnosed for years. Clues that something more is going on include sleepiness that persists despite a full night in bed, unusual movements or behaviors during sleep that a partner notices, and symptoms that started or worsened alongside a new medicine or pregnancy. A sleep diary and a description from anyone who sees you sleep are often the most useful things you can bring to an appointment, and your doctor can refer you to a sleep medicine specialist when needed.

Shift work, jet lag and naps

Some sleep problems come not from the brain or the bedroom but from asking the body clock to do something it was not built for. The same principles apply to all of them: light timing moves the clock, sleep pressure can be managed with well-placed naps, and caffeine is best used early and sparingly. None of these situations is fully fixable, especially rotating shifts, but the gap between a well-managed and a badly managed schedule is large, and it shows up in mood, safety on the road and how well you function at work.

Shift work

Night work asks you to be alert at the low point of your circadian cycle and to sleep at its high point. Discipline does not change that, but planning helps. A 20-30 minute nap before a night shift, bright light during the first half of the shift, and stopping caffeine in the final few hours of it all help. On the way home, sunglasses reduce the morning light that tells your brain it is daytime. Make the bedroom genuinely dark, tell your household when your sleep window is, and nap before driving home if you feel sleepy. Report safety-critical sleepiness to your employer.

Jet lag

Jet lag is the mismatch between your body clock and local time after crossing time zones. Adjustment takes roughly a day per time zone crossed, and traveling east, which shortens your day, is usually harder than traveling west. After flying east, seek morning light at your destination and avoid bright evening light; after flying west, do the opposite. Switch meals and activity to local time from arrival, avoid alcohol on the flight, and keep any nap on arrival short. On long flights, move your legs regularly, and get prompt care for calf pain or swelling afterward.

Naps

A nap of 10-20 minutes improves alertness without much grogginess. Naps of 30-60 minutes often leave you groggy because you wake from deep sleep, while about 90 minutes allows a full cycle. The early afternoon, roughly 1 p.m. to 3 p.m., suits most people; late naps use up sleep pressure you need that night. If you have insomnia, it is usually better not to nap at all. A persistent need to nap despite enough time in bed is a symptom worth getting checked, not a habit to accept.

Sleep through the stages of life

Sleep needs and sleep problems change across a lifetime. Most of the principles in this guide apply at every age, but a few groups need specific advice, and for some of them standard adult advice is not safe. Sleep restriction, sleep medicines and supplements in particular need a different approach for babies and children, during pregnancy and in later life, so check the notes below before applying the rest of this guide to someone in these groups.

Babies and children

For babies, the American Academy of Pediatrics advises placing them on their back for every sleep, on a firm, flat surface in their own crib or bassinet, with no pillows, bumpers, blankets or soft toys. Room-sharing without bed-sharing is recommended. For older children, a consistent bedtime routine in the same order every night, a dim and screen-free bedroom, and a regular wake time solve most problems. Children who snore loudly most nights, gasp or pause in their sleep, or seem persistently sleepy or hyperactive should see their doctor, as childhood sleep apnea is often linked to enlarged tonsils.

Teens

Teens need 8-10 hours, and their later body clocks make that hard on school nights. Keeping phones out of the bedroom overnight, getting morning light, keeping weekend wake times within an hour or two of weekday ones, and avoiding caffeinated sodas and energy drinks all help. Persistent sleepiness despite reasonable sleep, or a sleep pattern tied to low mood, is worth raising with a doctor.

Pregnancy and menopause

Pregnancy brings discomfort, heartburn, frequent urination and, for some, restless legs and snoring. Sleeping on your side in later pregnancy is commonly advised; ask your prenatal care provider about your own situation, keep caffeine below 200 mg a day, and check with them before taking any sleep aid or supplement. Around menopause, hot flashes and night sweats often break sleep, and the risk of sleep apnea rises. Both are worth discussing with your doctor because effective options exist.

Older adults

Sleep tends to become lighter and earlier with age, but persistent poor sleep is not an inevitable part of aging. Pain, nighttime urination, medicines and sleep apnea are common and treatable causes. Older adults are particularly vulnerable to the side effects of sleep medicines, including confusion and falls at night, so non-drug approaches such as CBT-I are especially valuable. Napping late in the day, spending long hours in bed and getting little daylight are common in retirement and can all weaken the body clock signal, so a regular wake time, time outdoors in the morning and daytime activity often help more than anything taken at bedtime.

Sleep medicines, supplements and their risks

Over-the-counter sleep aids in the US usually contain an antihistamine such as diphenhydramine or doxylamine. They can cause next-day drowsiness, dry mouth, constipation and difficulty urinating, and they are a particular concern for older adults because of confusion and falls. Tolerance develops quickly, so they are not a solution for chronic insomnia. Check with a pharmacist before using them if you take other medicines, have glaucoma, an enlarged prostate or breathing problems, or are pregnant or breastfeeding.

Melatonin is sold in the US as a dietary supplement. Supplements are not approved by the FDA for safety and effectiveness before they are sold, and the amount in a product may not match the label. Melatonin can help with some body clock problems, such as jet lag and delayed sleep phase, but evidence for general insomnia is limited. Talk to your child's doctor before giving it to a child, and store gummies out of reach: they look like candy.

Prescription sleep medicines can help in the short term for some people, but they carry real risks, including next-morning impairment that can affect driving. The FDA requires a boxed warning on eszopiclone, zaleplon and zolpidem because of rare but serious injuries from complex sleep behaviors such as sleepwalking and sleep-driving. Never combine sleep medicines with alcohol, opioids or other sedatives. If someone may have taken too much, call Poison Control at 1-800-222-1222, or 911 if they are hard to wake or breathing slowly.

Common myths and what the guidance says

Sleep attracts more folk wisdom than almost any other area of health, and some of it actively makes things worse. The most damaging myths tend to encourage spending more time in bed, sleeping in, or treating sleepiness as a sign of commitment rather than a health signal. Others are half true: they describe something that helps a little, such as a cool bedroom, and present it as a cure. Here are the ones that come up most often, set against what US sleep guidance actually says.

• Myth: you can train yourself to need less sleep. Guidance: most adults need 7 or more hours, and the effects of short sleep build up even when you stop noticing them.
• Myth: going to bed early makes up for a bad night. Guidance: it usually means more time lying awake; keep your normal schedule and wake time.
• Myth: a nightcap helps you sleep. Guidance: alcohol fragments the second half of the night.
• Myth: loud snoring is harmless. Guidance: with pauses, gasping or daytime sleepiness it can signal sleep apnea and needs checking.
• Myth: weekend lie-ins repay the week's debt. Guidance: large swings in wake time act like jet lag; a consistent schedule works better.
• Myth: if you cannot sleep, stay in bed and keep trying. Guidance: after about 20 minutes awake, get up until you feel sleepy.
• Myth: melatonin is a harmless natural sleeping pill. Guidance: it is a hormone, products vary, and it should be discussed with a doctor, especially for children.

Talking to your doctor and a 4-week plan

Before an appointment, keep a sleep diary for one to two weeks: when you went to bed, roughly when you fell asleep, night wakings, when you got up, naps, caffeine, alcohol and how you felt during the day. Ask a bed partner whether you snore, stop breathing or kick. Bring a list of your medicines and supplements. Useful questions include whether you should be tested for sleep apnea, whether CBT-I is available through your plan or a digital program, and whether any of your medicines might be affecting your sleep.

Coverage varies. Many insurance plans and Medicare cover sleep studies and CPAP when they are medically necessary, though copays apply and insurers commonly expect evidence that you are using CPAP regularly during an initial period. Ask about costs before a test, and ask whether a home sleep study is an option, since it is usually cheaper and more convenient than an overnight lab study.

The plan below works for most adults with everyday sleep problems. It is not a substitute for assessment if you have signs of sleep apnea, severe daytime sleepiness or insomnia lasting three months or more. Treat it as an experiment: change one or two things each week, keep the diary going so you can see what actually made a difference, and expect improvements to build over weeks rather than overnight. The first week of a fixed wake time is often the hardest.

• Week 1: pick a fixed wake time for all 7 days, get outside within a couple of hours of waking, and start a sleep diary
• Week 2: set a caffeine cut-off in the early afternoon, stop alcohol within a few hours of bed, and dim the lights for the last hour of the evening
• Week 3: use the bed only for sleep and sex, get up after about 20 minutes awake, and move the phone charger out of the bedroom
• Week 4: review the diary; if you are still sleeping poorly, snoring loudly or sleepy in the day, book an appointment and take the diary with you

Every guide in this topic

• What the Guidance Really Says About Insomnia
• Sleep Apnea: What the Evidence Actually Says
• Caffeine and Sleep: Sorting the Evidence From the Noise
• Shift Work and Sleep: Sorting the Evidence From the Noise
• Napping: What Published Guidance Supports
• The Body Clock: Sorting the Evidence From the Noise
• The Sleep Environment: What Published Guidance Supports
• Sleep and Physical Health: What the Evidence Actually Says
• The Evidence on Sleep in Children, Without the Hype
• Jet Lag: Sorting the Evidence From the Noise

Frequently asked questions

How many hours of sleep do adults really need?

The CDC and the American Academy of Sleep Medicine advise 7 or more hours a night for adults, with 7-9 hours for those aged 61-64 and 7-8 hours from 65. That is actual sleep, so allow a little more time in bed. If you regularly need an alarm, caffeine or weekend lie-ins to cope, you are probably getting less than you need.

Is it bad to wake up in the middle of the night?

Brief awakenings between sleep cycles are normal, and most people forget them. It becomes a problem when you lie awake for long periods, regularly, and feel the effects during the day. If that happens on 3 or more nights a week for 3 months or more, talk to your doctor about insomnia and ask about CBT-I.

What should I do if I cannot fall asleep?

If you have been awake about 20 minutes, get out of bed and do something quiet and dull in dim light, then return when you feel sleepy. Avoid checking the clock or your phone. Keep the same wake time the next morning however the night went. Over time this teaches your brain to associate bed with sleep rather than frustration.

How late can I drink coffee?

Caffeine stays active for several hours and the time varies widely between people, so there is no single safe cut-off. Early afternoon suits most people who sleep poorly. Count tea, cola, energy drinks and chocolate too. Healthy adults should stay under about 400 mg a day, and under 200 mg in pregnancy.

Is snoring a sign of sleep apnea?

Not always, but loud snoring combined with pauses in breathing, gasping or choking, or daytime sleepiness should be checked. Sleep apnea is linked to high blood pressure, atrial fibrillation, stroke and drowsy-driving crashes. Diagnosis usually involves a sleep study, which can often be done at home, and effective treatments are available.

Is melatonin safe to take?

Melatonin is sold as a dietary supplement in the US, so products are not FDA-approved for safety and effectiveness and doses may not match the label. It can help some body clock problems, such as jet lag, but the evidence for general insomnia is limited. Talk to your doctor first, and always talk to your child's doctor before giving it to a child.

Are over-the-counter sleep aids a good idea?

They usually contain antihistamines such as diphenhydramine, which can cause next-day drowsiness, confusion and falls, especially in older adults, and they lose effect quickly. They are not a treatment for chronic insomnia. Ask a pharmacist before using one, particularly if you take other medicines, are pregnant, or have glaucoma, prostate or breathing problems.

Can I catch up on sleep at the weekend?

A little extra sleep after a hard week can help you feel better, but sleeping in by several hours shifts your body clock later and makes Sunday night and Monday morning harder, much like jet lag. A consistent wake time across the week, with enough sleep every night, works better than trying to repay a large debt in one go.

How can I help my teenager get more sleep?

Teens need 8-10 hours, but their body clocks naturally shift later. Help them keep phones out of the bedroom overnight, get morning daylight, limit caffeinated sodas and energy drinks, and keep weekend wake times close to weekday ones. Talk to their doctor if sleepiness persists, they snore loudly, or poor sleep comes with low mood.

When is daytime sleepiness a medical problem?

If you fall asleep without meaning to, need daily naps despite enough time in bed, or feel sleepy while driving, see your doctor. Possible causes include sleep apnea, narcolepsy, medicines, depression, anemia or thyroid problems. Until you have been assessed, do not drive when sleepy, and pull over somewhere safe if drowsiness hits on the road.

When to speak to a doctor

See your doctor if poor sleep has lasted three months or more, if you snore loudly with pauses or gasping, if you fall asleep without meaning to during the day, or if sleep problems come with low mood or anxiety. Do not drive when you are sleepy. Call 911 if someone cannot be woken, is breathing slowly or abnormally, or has chest pain or signs of stroke. If someone may have taken too much of a sleep medicine or melatonin, call Poison Control at 1-800-222-1222. If you are having thoughts of harming yourself, call or text the 988 Suicide & Crisis Lifeline.

Where this comes from

• American Academy of Sleep Medicine — Healthy Sleep Habits
• CDC — How Much Sleep Do I Need?
• National Heart, Lung, and Blood Institute — Insomnia
• National Heart, Lung, and Blood Institute — Sleep Apnea
• American Academy of Pediatrics — Healthy Sleep Habits: How Many Hours Does Your Child Need?
• FDA — Spilling the Beans: How Much Caffeine Is Too Much?
• American College of Obstetricians and Gynecologists — Moderate Caffeine Consumption During Pregnancy
• NIOSH — Work Schedules: Shift Work and Long Work Hours
• CDC — Jet Lag
• FDA — FDA adds Boxed Warning for risk of serious injuries caused by sleepwalking with certain prescription insomnia medicines

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.