Why do we dream?
In fact, even science has not found a clear answer yet.Why we dream is still not clearly understood. Most dreams happen during REM sleep, when the brain is very active even though we are asleep. A US national research institute says dreaming may help us process our emotions, and some studies link dreams to sorting memories, but there is no proven answer yet.
Two kinds of sleep
There are two kinds of sleep: REM sleep and non-REM sleep. During REM sleep, the eyes move quickly behind closed eyelids (REM stands for "rapid eye movement"). According to the US National Institute of Neurological Disorders and Stroke (NINDS), REM sleep first begins about 90 minutes after we fall asleep, and it takes turns with non-REM sleep many times through the night. During REM sleep, brain activity becomes closer to that of being awake.
Most dreams happen in REM sleep
Most dreams happen during REM sleep, but we can also dream during non-REM sleep. According to an explainer from Macquarie University in Australia, up to 95% of people woken during REM sleep say they were dreaming, compared with only about 5-10% of people woken during other stages of sleep. During REM sleep, the muscles of the arms and legs are temporarily unable to move, so even if you run in a dream, your body does not actually get up and move.
Based on an explainer from Macquarie University, Australia.
What dreams are for is still being studied
NINDS says the exact purpose of dreaming is not known, but that it may help us process our emotions. Because events from the day often show up in dreams, some researchers think dreaming is linked to sorting memories. A 2019 paper brought together research suggesting that REM dreams may help soften the feelings attached to painful experiences. There is also the idea of the psychologist Sigmund Freud that dreams express hidden wishes, and researchers are still debating it.
We dream every night
According to NINDS, everyone dreams. We spend about 2 hours dreaming each night, but we may not remember most of our dreams. People dealing with stress or worry are more likely to have frightening dreams. Dreams are usually most vivid during REM sleep, and some people dream in color while others only remember dreams in black and white.
Want to know more?
- REM sleep periods get longer as morning gets closer.
- About two-thirds of dreams feature people we know, and family members appear in about 20% of dream reports.
- Some people who have lost REM sleep because of damage to part of the brain still report dreaming, so dreams and REM sleep are not thought to be exactly the same thing.
Quick quiz: test yourself
During which kind of sleep do most dreams happen?
Show the answer
- REM sleep
- Deep non-REM sleep
- Light sleep just after dozing off
REM sleep Most dreams happen during REM sleep, when the brain works in a way close to being awake. Dreams can also happen during non-REM sleep.
Most dreams happen during REM sleep, when the brain works in a way close to being awake. Dreams can also happen during non-REM sleep.
Next quiz ›Sources
- Brain Basics: Understanding SleepNINDS（アメリカ国立神経疾患・脳卒中研究所）
- Why do we dream?Macquarie University（マッコーリー大学）The Lighthouse
- Dream (sleep experience)Encyclopaedia Britannica（ブリタニカ百科事典）
- The Functional Role of Dreaming in Emotional ProcessesFrontiers in Psychology（PMC 掲載の査読論文）
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
