Adults typically should aim for about 20-25% of their total sleep time to be REM sleep. For someone getting the recommended 7-8 hours of sleep per night, this translates to roughly 90 minutes to 2 hours of REM sleep. REM sleep usually starts about 90 minutes after falling asleep and occurs in cycles that get longer through the night, with the final cycle lasting up to an hour. Lack of sufficient REM sleep can impair brain functions like memory and emotional regulation and is linked to negative health outcomes such as increased risk for obesity, diabetes, depression, and cardiovascular issues. Therefore, ensuring adequate total sleep duration helps secure enough REM sleep naturally.