Last updated: August 2026
REM sleep is the stage when you dream, when your brain is almost as active as it is awake, and when a night's worth of memories and emotions get filed. It is also the stage a short or broken night costs you first, because most of it happens in the hours before you wake.
Quick answer: REM (rapid eye movement) sleep is the fourth stage of the sleep cycle, when the eyes dart under the lids, the brain becomes highly active and the body's muscles are switched off; it makes up around 20 to 25% of an adult's night and is when most vivid dreaming happens. It matters because it is when the brain consolidates memories and processes emotion, which is why a night short on REM leaves you forgetful and irritable. REM comes in longer bursts towards morning, so waking early, sleeping hot, or drinking alcohol late all cut it disproportionately.
What is REM sleep?
REM sleep is the stage of sleep in which the eyes move rapidly beneath closed lids, brain activity rises to near-waking levels and the major muscles are temporarily paralysed. It was identified in 1953 by Eugene Aserinsky and Nathaniel Kleitman at the University of Chicago, who noticed sleeping subjects' eyes moving in bursts and found that waking them then produced detailed dream reports.
Because the brain looks awake while the body is switched off, researchers called it paradoxical sleep. The muscle paralysis, called atonia, is what stops you acting out your dreams, and heart rate, breathing and blood pressure all become more variable than in the deeper stages.
What are the stages of sleep?
A night's sleep runs in cycles of about 90 minutes, each moving through three stages of non-REM sleep and then a period of REM, and you complete four to six cycles a night. The Sleep Foundation describes the sequence as N1 (dozing off, a few minutes), N2 (light sleep with a drop in temperature and heart rate, about half the night), N3 (deep, slow-wave sleep, when tissue repair and immune work happen) and then REM.
The first REM period arrives about 90 minutes after you fall asleep and lasts only a few minutes. Each cycle's REM period is longer than the last, so by the early hours you may spend half an hour or more in REM at a stretch. Deep sleep works the other way, concentrated in the first half of the night.
That distribution is the practical point. If you sleep six hours instead of eight, you do not lose a quarter of each stage; you lose the last two cycles, which are mostly REM. Newborns spend around half their sleep in REM, and the proportion falls through childhood to the adult 20 to 25%.
Why is REM sleep important?
REM sleep matters because it is when the brain consolidates what you learned during the day and takes the emotional charge out of what happened to you. Cut it short and both suffer: recall is worse the next day, and small setbacks feel bigger.
The emotional role has the strongest evidence. A 2009 review in Psychological Bulletin by Matthew Walker and Els van der Helm described REM sleep as a form of overnight therapy, in which the brain replays emotional experiences while the stress chemistry that accompanied them is switched off, so you wake with the memory but less of the sting. It is also the stage most associated with creative problem solving, the reason answers sometimes arrive in the morning.
The stage is self-correcting to a degree. After a night with little REM the brain schedules more the following night, called REM rebound, which is why the first night after a late one is often full of vivid dreams. Rebound repairs a bad night; it does not cover a chronic shortfall.
What happens when we dream?
Everyone dreams, several times a night, whether or not they remember it. Most vivid, story-like dreams happen in REM, when the visual and emotional parts of the brain are active and the logical, planning areas are quieter, which is why dreams feel real at the time and absurd afterwards. Recall depends on when you wake: surface from REM and the dream is fresh, wake from deep sleep and it is gone.
Dreams can colour the day. In a series of studies published in 2009, Morewedge and Norton found that people said a dream about a plane crash the night before a flight would make them more likely to cancel than an official warning would, so a bad dream is worth noticing and then discounting. If you want to remember more, keep a notebook by the bed and write the moment you wake, before the memory fades.
Lucid dreaming, being aware you are dreaming while it happens, is a learnable skill for some people. The usual approach is a dream journal to improve recall, regular reality checks during the day (asking whether you are dreaming until the habit carries into sleep), and a consistent schedule so the long morning REM periods are not cut off by the alarm.
What reduces REM sleep?
Alcohol is the biggest everyday REM thief. A 2013 review in Alcoholism: Clinical and Experimental Research found that alcohol before bed reduces REM sleep in the first half of the night at every dose studied, and disrupts sleep in the second half as it wears off, which is why a few drinks give a deep-seeming start and a fragmented, dream-poor finish.
Anything that ends the night early or breaks it in the early hours costs REM too: an early alarm, a partner turning over, a hot room, a dip in the mattress that wakes you to shift position. Caffeine late in the day, some antidepressants and untreated sleep apnoea also reduce it, and if you snore heavily and wake unrefreshed, apnoea is worth ruling out with a GP. Our guide on how to stay asleep all night covers the early-hours wakings.
How do you get more REM sleep?
Sleep longer and sleep through: REM cannot be targeted directly, but because it is concentrated at the end of the night, the two things that reliably increase it are a full seven to nine hours and an uninterrupted final third. A fixed wake time, no alcohol in the six hours before bed and a cool, dark room do most of the work, and our guide on falling asleep fast covers the start of the night.
The bed matters more for REM than for any other stage, because the early hours are when it is lightest and easiest to break. A mattress that runs warm, transfers a partner's movement, or dips so you wake to reposition takes its toll exactly when the long REM periods are due. Every one of REM-Fit's pocket sprung and memory foam hybrid mattresses is built to hold that final third: tall pocket springs that move independently so movement stays on one side, open-cell memory foam that lets air pass through the foam so heat does not build up, and zoned support so you are not shifting to relieve pressure.
The REM-Fit 5000 Lux Elite goes furthest, with 5000 tall premium pocket springs in two layers for the best motion isolation in the range and the deepest open-cell layer for hot sleepers, at a medium-firm 7.5 out of 10. It is Good Housekeeping Approved 2026, and Good Housekeeping's reviewers singled out its cooling.
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Why is REM-Fit called REM-Fit?
Because the stage is the point. The brand took its name from REM sleep on the principle that a mattress is only doing its job if it lets you reach and hold the deepest and most restorative parts of the night, and the name has stuck since the early days when REM-Fit made sleep trackers as well as beds. In 2018 the brand sponsored The Art of Dreaming, an evening at the Freud Museum in London with dream researcher Dr Keith Hearne, one of the first scientists to record a lucid dream in a laboratory.
REM sleep FAQs
Last updated: August 2026
How much REM sleep do you need?
Around 20 to 25% of the night for an adult, which is roughly 90 minutes to two hours in an eight-hour sleep. You cannot dose it directly; you get it by sleeping a full night and not breaking the final third, when the longest REM periods fall.
What happens if you do not get enough REM sleep?
Memory for what you learned the day before is worse, mood is flatter and more reactive, and concentration drops. The brain compensates with extra REM the following night (REM rebound), so an occasional short night is repaired, but a chronic shortfall is not.
Is REM sleep the same as deep sleep?
No. Deep sleep is stage N3, slow-wave sleep, when the body repairs tissue and the brain is at its quietest, and it comes mostly in the first half of the night. REM is the active, dreaming stage that comes mostly in the second half, and you need both.
Does alcohol affect REM sleep?
Yes. A 2013 review found alcohol before bed reduces REM in the first half of the night at every dose studied and fragments sleep in the second half. Stop drinking at least six hours before bed if you want to keep your REM.
Can you dream without REM sleep?
Yes, but differently. Dreams in non-REM sleep tend to be brief and thought-like; the vivid, story-like dreams people remember almost all come from REM, which is why you recall a dream when you wake from it and not when you wake from deep sleep.
Sources: Sleep Foundation, Stages of Sleep; Aserinsky and Kleitman, Regularly occurring periods of eye motility during sleep, Science, 1953; Walker and van der Helm, Overnight therapy? The role of sleep in emotional brain processing, Psychological Bulletin, 2009; Ebrahim et al., Alcohol and sleep I: effects on normal sleep, Alcoholism: Clinical and Experimental Research, 2013; Morewedge and Norton, When dreaming is believing, Journal of Personality and Social Psychology, 2009.
