Why we dream — and why we forget our dreams by morning

Everyone dreams. According to the US NINDS, we spend about two hours every night dreaming, but we don't remember most of our dreams. The exact purpose of dreaming isn't known; it may help us process emotions. (NINDS — Brain Basics: Understanding Sleep)

This article explains what research has shown so far; it is not a diagnosis or a treatment.

When in the night we dream

According to the NHLBI, dreaming usually happens in REM sleep: your eyes twitch behind closed lids, your brain is active much as it is when you are awake, and your muscles go limp so that you don't act out your dreams. REM sleep increases later in the night. (NHLBI — Sleep Phases and Stages) NINDS adds that dreams can occur in all stages of sleep, but they are usually most vivid in REM. (NINDS — Brain Basics: Understanding Sleep)

A study in Nature Neuroscience (2017) supported this in the lab: volunteers (32 healthy people in the first experiment) were woken repeatedly while their brains were recorded with high-density EEG. Dreams also occurred outside REM. In both types of sleep, dreaming was linked to reduced slow activity in the back of the cerebral cortex — the authors called it a "hot zone". In a further experiment, monitoring this area in real time let them predict whether a person woken from non-REM sleep would report a dream. (Siclari et al., Nature Neuroscience 2017)

Why we usually don't remember our dreams

In the same study, people sometimes said that they had dreamed something but could not recall the content. (Siclari et al., Nature Neuroscience 2017)

Another study (Neuropsychopharmacology, 2014) used PET to compare people who often remember their dreams with people who rarely do; 37 people fell asleep in the scanner. Frequent recallers had higher activity in some brain regions both asleep and awake. The authors suggest that this may make them wake briefly more often during the night — and that brief waking may help store a dream in memory. This is a hypothesis, not a proven mechanism. (Eichenlaub et al., Neuropsychopharmacology 2014)

How often you remember dreams therefore varies between people; the cited studies do not describe it as a sign of illness.

What dreams are for

• The exact purpose of dreams isn't known; dreaming may help process emotions. (NINDS — Brain Basics: Understanding Sleep)
• Events from the day often find their way into dreams, and people with stress or anxiety are more likely to have frightening dreams. (NINDS — Brain Basics: Understanding Sleep)
• None of the cited sources supports reading dreams with a dream dictionary.

When to see a doctor

• Nightmares, according to the NHS, are bad dreams you wake up from and can remember; both children and adults have them. If you have regular nightmares that affect your sleep and everyday life, see a GP; for frequent nightmares, cognitive behavioural therapy (CBT) can help. (NHS — Night terrors and nightmares)
• The NHS also advises seeing a GP if changing your sleeping habits has not helped, you've had trouble sleeping for months, or insomnia is affecting your daily life. (NHS — Insomnia)
• An AI health check is not a medical review. This article is not medical advice.

Takeaways

1. Everyone dreams, for about two hours a night — but we forget most dreams.
2. The most vivid dreams come in REM sleep, which increases towards morning; we also dream in other stages.
3. In the lab, activity in a "hot zone" at the back of the brain could predict whether a person would report a dream on waking.
4. According to one small study, frequent dream recallers show different brain activity; brief night-time awakenings may play a part.
5. Regular nightmares that spoil your sleep and day → doctor; CBT can help.

Dreams remain one of the least explored parts of the night — and not remembering them is completely normal.