Deep sleep vs REM: what's the difference, and how much do you need?
A night's sleep cycles through light sleep, deep (slow-wave) sleep and REM sleep. Deep sleep is when your body does most of its physical repair — muscle recovery, immune function, hormone release. REM sleep is when the brain consolidates memory and regulates emotion. Most adults spend roughly 13–23% of the night in deep sleep and 20–25% in REM, cycling every ~90 minutes.
What each stage does
Deep sleep dominates the first half of the night and drives physical recovery; skimping on it leaves you feeling physically unrestored. REM concentrates in the second half and handles memory and mood — which is why cutting your night short (and losing that late REM) hurts focus and emotional balance. You need both, in proportion, not just total hours.
How Vita shows your sleep stages
Vita reads your sleep structure from WHOOP or Apple Watch and shows the deep / REM / light split per night alongside efficiency, consistency and sleep debt — so instead of just 'you slept 7 hours', you see whether the quality of that sleep actually supports recovery.
FAQ
Is deep sleep or REM more important?
Both matter and you can't substitute one for the other — deep sleep restores the body, REM restores the brain. Healthy sleep has enough of each in proportion.
How much deep sleep do I need?
Roughly 13–23% of total sleep for most adults, though it declines with age. The trend versus your baseline matters more than hitting an exact number.
Why is my REM low?
Alcohol, late caffeine, stress and short sleep all suppress REM — and because REM concentrates late in the night, waking early cuts it disproportionately.