REM rebound is the lengthening and increasing frequency and depth of REM sleep which occurs after periods of sleep deprivation. When people are prevented from experiencing REM, they take less time than usual to attain the REM state.[1]
Common to those who take certain sleeping aids, it is also often seen in the first few nights after patients with obstructive sleep apnea syndrome 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 4 to 5 hours after sleep onset.[2]