REM rebound

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REM rebound is when you spend more time in REM sleep after you’ve had sleep loss. If REM is blocked, you reach REM faster when you finally sleep, and once you can sleep normally again you spend a larger share of the night in REM.

Early studies showed REM makes up about 20% of sleep. In REM deprivation experiments, people were woken whenever REM began. After several nights, those who could sleep freely showed REM rising from about 19% to about 27% of total sleep, more than a control group woken at random times. The deprived subjects also became irritable, anxious, and hungry.

REM rebound shows the brain needs REM sleep to function properly. In some animals, like dolphins and fur seals, only the deprived hemisphere shows REM rebound when one brain half is restricted.

REM rebound is common with certain sleep aids and is often seen in the first nights after starting CPAP for sleep apnea.

Alcohol suppresses REM in the first half of the night, then can cause a rebound about 4–5 hours after sleep starts. It may help you fall asleep faster but disrupts sleep cycles, lowering REM early and increasing lighter sleep later.

Many antidepressants, especially SSRIs such as citalopram and paroxetine, suppress REM sleep and can cause REM rebound when stopped.