Sleep & mental health

Stage 1 is the bridge between being awake and being asleep. It usually lasts only a few minutes and makes up about 5% of the night. It’s easy to be woken from this stage, and you might not even feel you were asleep.

That “falling” jolt some people feel as they drift off, or a sense that you only “rested your eyes”, often happens in this light stage.

In stage 2 you are properly asleep. Brain waves slow down, with short bursts of activity in between. Experts think these bursts help organise memories. Stage 2 makes up about 45% of the night, more than any other stage.

Your heart rate and blood pressure drop during non-REM sleep, giving your heart a lighter workload for a while.

Deep sleep, also called slow-wave sleep, is the stage your body uses to repair itself and support your immune system. You need enough of it to wake up feeling rested. In adults it makes up about a quarter of the night.

Your body tries to get deep sleep early, so most of it happens in the first part of the night. It’s hard to wake someone from deep sleep, and if you are woken, you may feel groggy or foggy for around 30 minutes. This is called sleep inertia.

Deep sleep peaks in early childhood, drops sharply in the teen years and keeps declining through adulthood. Some older people get little or none, which is one reason sleep can feel lighter with age.

In REM sleep your eyes move quickly behind closed lids and your brain is about as active as when you’re awake. This is when most dreaming happens. Your muscles usually go limp, which stops you from acting out your dreams.

The first REM period of the night is short, about 10 minutes. Later ones grow longer, up to about an hour. REM makes up about a quarter of the night in adults, and newborns spend even more time in it.

Because REM comes mostly in the second half of the night, cutting your sleep short in the morning tends to cut REM sleep too. Your body also doesn’t control its temperature well in REM, which is one reason a very cold room can disturb it.

At the end of a cycle, you may wake up for a moment before the next cycle begins. Most of the time you won’t remember it. Moving around a bit in the night is normal too.

Knowing this can take the fear out of night waking. Waking at 3 a.m. doesn’t mean your night is ruined. It may simply be the gap between two cycles.

Pressure to sleep builds with every hour you’re awake and peaks in the evening. One chemical linked to this is adenosine. Its level in the brain rises while you’re awake, and your body breaks it down while you sleep.

This is why long naps or lying in late can make it harder to fall asleep that night: they let off some of the pressure you need at bedtime.

Your body clock is controlled by a master clock in the brain called the suprachiasmatic nucleus (SCN). It keeps the clocks in your organs and tissues in step with each other.

Light and darkness have the biggest effect on it. Food, stress, physical activity, your social life and temperature play a part too. Your body clock shapes not only sleep, but also hormones, appetite, digestion and body temperature.

In the morning, a stress hormone called cortisol rises with the sun and helps you wake. As it gets dark, your body sends out its natural “time to sleep” signal.

Your natural preference for early or late sleep is called your chronotype. It’s mostly set by your body clock, shaped by both your genes and your surroundings. Most people fall somewhere in the middle, with “larks” and “owls” at either end.

Being a night owl is not a character flaw or laziness. It’s a real difference in timing. It can, though, be hard to live as an owl in a world built around early starts.

Clues to your chronotype

• When do you fall asleep and wake on free days, with no alarm?
• When in the day do you feel sharpest?
• How hard is it to wake for early starts?

Social jet lag is the gap between your body’s timing and the timing your life demands. Many people sleep short on work or school days, then catch up on free days. It can feel like flying across time zones every weekend.

Late chronotypes feel this most. In a 2006 study of 501 people, social jet lag was linked to poorer wellbeing and to more use of caffeine, nicotine and alcohol. These links were strongest in teens and young adults up to age 25.

Ways to shrink the gap

• Keep your weekend wake time within about an hour of your weekday one
• Get daylight soon after waking, especially on Monday mornings
• If you want an earlier bedtime, move it a little at a time rather than all at once

Teens’ bodies send the “time to sleep” signal later in the evening, so they fall asleep later and sleep later in the morning. Older adults tend to go to bed and wake up earlier.

Communities can work with this. When Seattle’s school district moved secondary school start times nearly an hour later, a study found students slept a median of 34 minutes more each day, with better attendance and a 4.5% rise in median grades.

When you’re short on sleep, you may feel frustrated, cranky or worried, especially around other people. It can also be harder to read other people’s emotions and reactions, which can lead to misunderstandings.

Ongoing poor sleep is linked to depression. Children and teens who are short on sleep may feel angry or impulsive, have mood swings, or feel sad and unmotivated.

Sleep helps the brain store what you’ve learned. Good sleep is linked to better learning, problem-solving, attention, decision-making and creativity.

Without it, you may find it harder to learn, focus and react. Children who don’t get enough sleep may seem overly active, have trouble paying attention, or get lower grades.

Ongoing sleep deficiency is linked to heart disease, kidney disease, high blood pressure, diabetes, stroke and obesity.

It can also change how your immune system works, which may make it harder to fight off common infections. In children and teens, sleep supports healthy growth and development.

Sleep deficiency raises the risk of injury. Drowsy driving causes serious crashes and deaths. In older adults, poor sleep may raise the risk of falls and broken bones.

Tired people make more mistakes. Lack of sleep has played a part in serious accidents, including plane crashes and ship groundings.

People who are short on sleep may struggle to get along with others, and find it harder to cope with change. Tiredness can make us less patient and more likely to take things personally.

Going to bed and waking up at the same times each day trains your body clock. Try to keep weekends within about an hour of your weekday times. Late nights and long lie-ins can throw your body clock off, a bit like jet lag.

Wake time matters most. Even after a bad night, try to get up at your usual time, rather than sleeping in.

Light entering your eyes tells your brain it’s daytime. As it gets dark, your body naturally sends signals that help you feel sleepy. Bright light late in the evening can delay this.

Try this

• Get outside in daylight every day, especially in the morning
• Dim the lights in the hour before bed
• Keep your bedroom dark: curtains, blinds or an eye mask can help
• A small, dim night light is okay if you need one

Bright light from phones, tablets, computers and TVs can signal your brain to stay awake. Scrolling also keeps your mind busy and alert.

The CDC suggests stopping electronic devices at least 30 minutes before bed. NHLBI suggests avoiding bright screens for the whole hour before bed.

Ideas

• Charge your phone outside the bedroom
• Use an old-fashioned alarm clock
• Swap scrolling for a book, puzzle or calm music
• Families: try a “screens to bed” basket where everyone’s devices go at night

Caffeine is a stimulant found in coffee, tea, soda, energy drinks and chocolate. Its effects can last up to 8 hours, so an afternoon coffee can still keep you awake at bedtime.

Alcohol might make you drowsy at first, but it makes sleep lighter and more broken later in the night. The NHS suggests avoiding alcohol, tea and coffee within 6 hours of bed. Nicotine is a stimulant too.

Your body can’t go from busy to asleep in a moment. Use the hour before bed for quiet, relaxing activities. A warm bath, gentle stretches or relaxation exercises can help.

Wind-down ideas

• Warm shower or bath
• Reading something light
• Gentle stretching
• Calm music or a podcast with a timer
• Writing tomorrow’s to-do list
• Slow breathing

If you often lie in bed awake, scrolling, working or worrying, your brain starts to link bed with being awake. Using your bed only for sleep and intimacy helps rebuild the link between bed and sleep.

How to do it

• Only go to bed when you feel sleepy, not just tired
• If you can’t sleep, get up and do something calm in dim light
• Go back to bed when you feel sleepy again
• Avoid working, gaming or watching TV in bed

A quiet, cool, dark bedroom helps your body settle. Earplugs, an eye mask or thick curtains can help if your home is noisy or bright. A comfortable mattress, pillows and covers matter too.

Being physically active during the day helps you sleep better at night. But intense exercise right before bed can keep you up. NHLBI suggests finishing exercise 5 to 6 hours before bed if you struggle with insomnia.

Avoid heavy or large meals close to bedtime. A light snack is fine. Eating meals at regular times also helps your body clock.

Short daytime naps can improve alertness. For adults, NHLBI suggests keeping naps to no more than 20 minutes.

If you have trouble sleeping at night, limit naps or have them earlier in the afternoon, or skip them for a while. Napping is normal and healthy for young children.

The experts rated this one of the top myths. Falling asleep easily in any situation is more often a sign that someone is chronically short on sleep. Strong daytime sleepiness can also be a sign of sleep apnea.

Older adults tend to sleep less, and it’s not clear they need less. Some of the drop may come from health conditions that disturb sleep.

The CDC still recommends 7 to 8 hours for adults 65 and older, so it’s worth looking into sleep problems at any age.

Very long sleep has been linked with poorer health, though this may be because illness makes people sleep more. For people with insomnia, spending extra time in bed trying to catch up can make sleep lighter and more broken.

That’s why CBT for insomnia sometimes shortens time in bed at first, to rebuild a strong sleep drive.

One short night does affect attention and can raise blood pressure for a while. But performance generally returns to normal after you catch up on sleep. Ongoing short sleep is what affects long-term health.

Brain activity, hormones and body temperature change in different ways during sleep than during quiet rest. Resting calmly is still kinder than tossing and turning, but it doesn’t replace sleep.

If you’ve been lying awake and frustrated for a while, getting up to do something calm and coming back when sleepy usually works better than staying put.

Pressing snooze again and again breaks up light sleep at the end of the night. Broken sleep has been linked to poorer mood and less flexible thinking. The experts suggest setting one alarm for the time you actually need to get up.

Hot, stuffy bedrooms are linked to poor sleep. The experts note that a cooler range of about 65–70°F (18–21°C) is often recommended.

Very cold rooms can disturb sleep too, especially REM sleep, so aim for comfortably cool with covers you can adjust.

Watching TV late at night is more common in people who sleep too little. What you watch can stir up your mind and make it harder to fall asleep.

If you’ve had enough sleep, boredom doesn’t make you fall asleep. Feeling very sleepy in a dull meeting or class is often a sign you’re short on sleep.

People who are short on sleep may seem cranky, worried or easily upset, find it hard to focus, or nod off during the day without meaning to. In children it can look like being overly active, misbehaving or struggling at school.

They may not connect these changes to sleep. A gentle, curious question can open the door: “You seem worn out lately. How have you been sleeping?”

Helpful things to say

• “That sounds exhausting. How can I help today?”
• “Would it help if I took the morning shift?”
• “Do you want to talk, or would you rather have some quiet?”
• “Let’s try one small change together.”

Things that usually don’t help

• “Just go to bed earlier.”
• “I fall asleep as soon as my head hits the pillow.”
• “You’re just being lazy.”
• Asking “Did you sleep?” every single morning

Sleep naturally changes with age, but a sudden or big change is worth a gentle conversation. Poor sleep can go along with low mood, pain or other health changes, and an older person may talk about being tired rather than feeling low.

Poor sleep may raise the risk of falls in older adults, so practical safety at night matters too.

Practical help

• Add night lights on the way to the bathroom
• Invite them for morning walks to get daylight and movement
• Help them keep a sleep diary to take to appointments
• Offer to go with them to see their clinical provider

Supporting someone through broken nights, whether a baby, a partner with insomnia or a parent with dementia, can leave you running on empty. Your own sleep matters just as much.

Ideas

• Take turns with night duties where you can
• Ask family, friends or community groups for a night off
• Use earplugs or a separate room on your “off” nights
• Protect a short wind-down for yourself, even on hard days

Where to look next

• A child who wakes in fear, nightmares, snoring or pauses in breathing, shift work, jet lag: the Nightmares, shift work & sleep problems guide
• Lying awake for weeks or months, racing thoughts at night, CBT for insomnia: the Insomnia & trouble sleeping guide
• Low mood, worry or feeling hopeless: the “Depression: understanding it” and “Anxiety: understanding it” guides

If sleep problems keep going or affect daily life, offer to help them make an appointment with their clinical provider, or to go with them.

Families can agree on quiet hours, a screen curfew, and a calm evening routine. Keeping devices out of bedrooms helps children and teens get enough sleep.

Ideas

• A shared “devices go to bed” time
• Dim lights and lower voices after a set hour
• Respect each other’s sleep, especially shift workers and new parents

The American Academy of Pediatrics recommends that middle and high schools start no earlier than 8:30 a.m. In the 2011–12 school year, only 17.7% of U.S. public middle and high schools met this goal.

Parents, students and teachers can ask their school boards about start times, homework load and sleep education.

Employers can help by giving workers enough time off between shifts to sleep, and by offering short, regular rest breaks during demanding work.

Teams can agree not to send messages late at night, so everyone can switch off.

If a friend seems exhausted, low or not themselves, a kind check-in can help. Offer to drive if they’re too sleepy, and encourage them to talk to a clinical provider if sleep problems keep going.