REM (Rapid Eye Movement) is a crucial stage of your nightly sleep related to memory and emotional processing.
During REM, the brain moves newly formed memories into long-term storage and works through emotional material.
While you remain fully asleep, your brain activity runs close to waking levels while the body stays still. REM is the stage where most dreaming happens.
Deep sleep focuses on the body’s physical repair, and most of the night’s growth hormone release . While a night short of deep sleep tends to register as physical tiredness, low REM sleep costs you on the cognitive and emotional side instead, which can feel like stress, or a bad mood, or simply a bad day.
This guide covers what REM does, where it sits in the night, and how much is normal at your age.
What happens during REM sleep
During REM, brain activity rockets while muscle activity is suppressed.
The autonomic pattern is distinctive too. In deep sleep, the parasympathetic “rest and digest” system dominates, and heart rate sits at its overnight low.
In REM, that shifts to a more mixed, variable profile – irregular beat-to-beat timing, with occasional brief movement.
What REM sleep does
Two functions have the most evidence behind them:
- Memory consolidation: Deep sleep appears to move newly formed memories from the hippocampus toward the cortex, while REM supports their consolidation there .
- Emotional processing: REM is the stage associated with working through emotionally charged material.
The most common cause of low REM
Sleep runs in roughly 90-minute cycles. Deep sleep dominates the first two. REM starts short – ten minutes or so – and lengthens with every cycle after.
That means your longest REM window comes right before you wake up. If you cut your sleep short by an hour, it disproportionately affects REM sleep. So ensuring your sleep duration is long enough to build longer REM sleep cycles is critical.
Duration is the big one, but not the only one. Alcohol, inconsistent drifting wake time, a warm bedroom, THC, SSRIs and some sleep aids, and untreated apnea all suppress REM sleep.
How much REM sleep is normal?
REM declines gradually across adulthood, so the useful comparison is your own age band. Below shows the average percentage of REM sleep from Ultrahuman users by age:
| Age band | Average REM (% of total sleep) |
|---|---|
| 18–29 | 23.3% |
| 30–39 | 22.4% |
| 40–49 | 21.6% |
| 50–59 | 21.0% |
| 60+ | 19.5% |
Source: Ultrahuman Ring data, 279,432 external members, March–June 2026. Women averaged 1.5 to 2.6 percentage points more REM than men across age bands.
This matches published sleep studies. A meta-analysis of 65 studies covering 3,577 healthy people aged 5 to 102 found REM percentage falls with age in adults, while lighter sleep and time spent awake increase.
However, your own trend over weeks is the more useful signal than any single night, partly because REM is also the hardest stage for a wearable to pin down precisely.
Frequently asked questions
What is REM sleep?
The stage of sleep where brain activity approaches waking levels while the body stays still. It’s when most dreaming happens, and it supports memory consolidation and emotional processing.
How much REM sleep should I get?
Across Ultrahuman Ring members, REM runs about 23 percent of the night in the 18 to 29 band and about 20 percent from age 60. On a 7.5-hour night, that’s roughly 90 to 105 minutes.
Why does REM happen mostly in the morning hours?
REM episodes lengthen with each successive sleep cycle, so the longest ones fall in the final cycles before waking. Deep sleep runs the opposite way, concentrated early.
Is REM more important than deep sleep?
They do different jobs – REM for memory and emotional processing, deep sleep for physical repair and growth hormone release – and the same habits protect both.
Does everyone dream in REM?
Most dreaming happens in REM, and most people dream every night whether or not they remember it. Dream recall depends largely on whether you wake during or shortly after a REM window.
References
- Diekelmann S, Born J. The memory function of sleep. Nature Reviews Neuroscience 2010;11(2):114–126. PMID 20046194
- Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals. Sleep 2004;27(7):1255–1273. PMID 15586779
- AlQatari AA, et al. Changes in heart rate variability and baroreflex sensitivity during daytime naps. Nature and Science of Sleep 2020. PMID 33061723
- Stich FM, Huwiler S, D’Hulst G, Lustenberger C. The potential role of sleep in promoting a healthy body composition. Neuroendocrinology 2021. PMID 34348331
[[Byline: medical reviewer TBC]] · [[Last updated: date]]
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