REM sleep (rapid eye movement sleep) is the sleep stage most closely associated with dreaming, characterised by rapid movements of the eyes beneath closed eyelids, increased brain activity, and temporary voluntary muscle paralysis. It plays a vital role in cognitive function, emotional regulation, and long-term health.
What happens during REM sleep
Despite the body being largely immobilised during REM, the brain is highly active — in many ways resembling wakefulness:
- Emotional processing — REM sleep is when the brain processes and integrates emotional experiences from the day. Insufficient REM sleep is linked to heightened emotional reactivity, irritability, and increased anxiety.
- Memory and learning — While deep sleep consolidates factual knowledge, REM sleep is critical for procedural memory (motor skills, technique) and creative problem-solving. Athletes learning new movement patterns benefit particularly from adequate REM.
- Brain development and maintenance — REM sleep supports neural plasticity, the brain's ability to form new connections and adapt. This is one reason infants and children spend a much larger proportion of sleep in REM than adults.
- Dreaming — Most vivid dreaming occurs during REM. While the exact function of dreams is debated, the REM stage itself is clearly essential for mental health.
REM sleep timing
REM sleep follows a pattern opposite to deep sleep. While deep sleep dominates the first half of the night, REM cycles grow longer toward morning. The first REM period may last only 10-15 minutes, while the final one before waking can extend to 30-60 minutes. This means that cutting your sleep short — whether by setting an early alarm or going to bed late — disproportionately sacrifices REM sleep.
How much REM sleep do you need?
Most adults spend approximately 20-25% of their total sleep time in REM, roughly 1.5 to 2 hours per night. Consistently falling below this range can impair cognitive performance, mood stability, and emotional resilience.
Factors that disrupt REM sleep
- Alcohol — One of the most potent REM suppressors. Even a couple of drinks significantly reduce REM sleep duration and quality.
- Cannabis — Regular use is associated with reduced REM sleep.
- Sleep deprivation — After missing sleep, your body prioritises deep sleep in recovery, often at the expense of REM.
- Early alarms — Waking before your body naturally finishes its sleep cycle cuts into the longest REM periods.
- Certain medications — Antidepressants and other medications can alter REM architecture.
Penng tracks your nightly REM sleep duration alongside light and deep sleep, giving you visibility into whether you are getting the balanced sleep your brain and body need.
Learn more about your health data — take the free quiz at penng.ai/quiz.