REM rebound

REM rebound is the lengthening and increasing frequency and depth of rapid eye movement (REM) sleep which occurs after periods of sleep deprivation. When people have been prevented from experiencing REM, they take less time than usual to attain the REM state.

Common to those who take certain sleeping aids, it is also often seen in the first few nights after patients with sleep apnea are placed on CPAP. Alcohol can also have an impact on REM sleep; it suppresses it during the first half of the night, leading to a rebound four to five hours after sleep onset.