<P> The fact that REM rebound exists shows that sleep and achievement of specific sleep stages are needed by the brain . In some marine animals, such as dolphins and fur seals, when one brain hemisphere is deprived of REM sleep, only the deprived hemisphere will go into REM rebound . The other hemisphere will be unaffected . </P> <P> REM rebound is common to those who take certain sleeping aids and it is also often seen in the first few nights after patients with sleep apnea are placed on CPAP . Alcohol can also affect REM sleep; it suppresses it during the first half of the night, leading to a rebound four to five hours after sleep onset . Although alcohol can decrease the amount of time it takes to fall asleep, it will cause a disruption in the sleep cycles . REM sleep is decreased during the first half of the sleep period and stage 1 sleep is increased in the second half of the sleep period . Most antidepressants, in particular selective serotonin re-uptake inhibitors (SSRIs), such as citalopram and paroxetine, are potent inhibitors of REM sleep and may also cause a REM rebound on discontinuation . </P>

The percentage of a nights sleep devoted to rem sleep