What REM sleep does for your brain

During REM the brain replays the day's experiences and integrates them with prior knowledge. Procedural memories (motor skills, language) consolidate in REM; declarative memories (facts) consolidate primarily in N3.

Suppressing REM with alcohol or certain antidepressants reduces creative problem-solving and emotional regulation the next day.

Most REM happens in the last third of the night. Cutting sleep short by 1–2 hours disproportionately costs you REM. Alcohol within 3 hours of bedtime suppresses REM in the first half of the night, even if you fall asleep quickly.