Dreams and Sleep: Cycles, REM Sleep and Basic Tips

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How a night of sleep is organised

Sleep is often thought of as a uniform state. In fact, it is made of cycles lasting about 90 minutes on average (60 to 120 depending on the person), which repeat three to six times a night. Each cycle includes light non-REM sleep, deep non-REM sleep, then REM sleep. Deep non-REM sleep dominates early in the night; REM sleep becomes longer towards morning, which explains why the longest and richest dreams unfold in the last hours.

Stage	Share of adult sleep	Characteristics
N1: falling asleep	4 to 5%	Transition lasting a few minutes; fleeting images, a feeling of falling
N2: light non-REM sleep	45 to 55%	Slower heart rate and breathing; brief dreams possible
N3: deep non-REM sleep	16 to 20%	Physical restoration; waking is difficult; night terrors and sleepwalking possible
REM sleep	20 to 25%	Active brain, rapidly moving eyes, nearly inert muscles; vivid dreams

These proportions are those published by Inserm for adults; they vary with age, and children have more deep sleep.

REM sleep: an awake brain in a motionless body

REM sleep is called “paradoxical” because the brain is almost as active as when awake while the body is deeply relaxed. The eyes move rapidly under the eyelids (hence the English name REM, for “rapid eye movements”), and the muscles are almost inert, except those of breathing and the eyes. This atonia prevents us from acting out our dreams.

In some people, often after the age of 50, this protective paralysis is absent: this is known as REM sleep behaviour disorder. The person shouts, lashes out, or falls out of bed while acting out their dreams, sometimes injuring themselves or their partner. This disorder requires specialist medical advice, as it can be an early sign of other conditions. Conversely, sleep paralysis, a brief inability to move when falling asleep or on waking, is harmless, even if it is frightening.

We also dream outside REM sleep

Experiments by Dement and Kleitman (1957) showed that volunteers woken during REM sleep reported a dream in the great majority of cases, far more often than during non-REM sleep. A major review of research (Nielsen, 2000) gives on average about 82% of dream reports after waking from REM sleep, and about 43% after non-REM sleep. The non-REM figure varies with the definition of a dream: if a simple thought or image counts, it rises; if a vivid story is required, it falls.

The takeaway is that “dreaming = REM sleep” is a shortcut. REM dreams tend to be more visual, strange and emotional; non-REM dreams are shorter and closer to thought. Finally, just as we fall asleep, many people see images (hypnagogic hallucinations), a kind of transition.

What dreams are for: what is debated

No one has yet demonstrated what dreams are for. The main hypotheses:

Hypothesis	Idea	Status
Activation-synthesis (Hobson and McCarley, 1977)	The brain makes sense of signals produced at random	Influential; since revised
Continuity (Domhoff, Schredl)	The dream extends the concerns of waking life	Well supported by the study of dream content
Threat simulation (Revonsuo, 2000)	The dream rehearses facing dangers	Only partly supported
Memory and emotions	Sleep fixes memories and regulates emotions	The role of sleep is supported; that of dreams remains debated
By-product	The dream has no function of its own	Possible, not demonstrated

These hypotheses are not mutually exclusive. The key point is that sleep is clearly useful (for memory, attention, mood and health), even if we do not know whether the content of dreams plays a role in this.

What influences dreams

• Stimulation during the night. A noise, thirst, heat or the need to urinate can be woven into a dream.
• Stress and emotions. Periods of tension are often accompanied by more numerous or more unpleasant dreams.
• Alcohol. It can reduce REM sleep early in the night and fragment sleep, then bring on intense dreams later.
• Lack of sleep. After a sleep debt, REM sleep tends to return with force (a “rebound”), with more intense dreams.
• Medications and substances. Some treatments (including some antidepressants) alter REM sleep; withdrawal from certain substances can cause very vivid dreams. Never change a treatment without medical advice.
• Meals, temperature, noise. A heavy meal or an overheated bedroom disrupt sleep, and therefore dreams.

Simple habits for better sleep

Here are basic guidelines, common in health recommendations. They do not replace medical advice.

1. Regular hours, including at weekends, without shifts of several hours.
2. Sufficient duration: at least 7 hours for most adults, with individual differences. According to Inserm, about one in three French adults (36% of those aged 18 to 75) sleeps less than 6 hours.
3. A quiet, dark and cool bedroom (18 to 19 °C is often cited), with a bed reserved for sleep.
4. Fewer screens in the evening. Light rich in blue delays falling asleep.
5. Caffeine, tobacco, alcohol: avoid caffeine in the late afternoon, and do not rely on alcohol to help you sleep.
6. A light evening meal and physical activity during the day, but not right before going to bed.
7. A short nap (15 to 20 minutes, early in the afternoon) if it does not disturb night-time sleep.
8. A calming ritual: reading, gentle stretching, slow breathing, dim lighting.

Keeping a sleep diary for a few weeks (times of going to bed, getting up and waking) helps identify irregularities, and it is useful to show a doctor if you consult one. See also remembering your dreams.

When to see a doctor

Talk to a doctor if you have difficulty falling asleep, or wake-ups that last for several weeks and affect your day; significant daytime sleepiness; snoring with pauses in breathing; legs that move or feel restless in the evening; violent behaviour or shouting during sleep; or nightmares that recur and exhaust you (see nightmares and night terrors). Sleep disorders are common and well treated; do not let them drag on.

If tiredness is accompanied by persistent sadness or dark thoughts, talk about it now. In France, 3114 (suicide prevention) answers free of charge, day and night; in an emergency, call 15, 17 or 112 (the emergency number across the European Union).

Frequently asked questions

Also read

The meanings mentioned belong to tradition and symbolism. They are neither promises of results nor medical advice. Back to Dream dictionary.