Sleep cycles consist of two main phases: rapid eye movement (REM) and non- rapid eye movement (NREM) sleep. A complete sleep cycle includes NREM stages 1, 2, and 3, followed by REM sleep. The body cycles through these stages approximately 4 to 6 times each night, with each cycle lasting about 90 to 120 minutes. Most people go through four or five cycles per night, assuming they get a full eight hours of sleep
. During REM sleep, most dreams occur, and the first REM cycle of a sleep period is typically the shortest, around 10 minutes, with each subsequent cycle having longer REM periods, up to an hour
. The NREM stages involve varying levels of depth, with the body repairing and regenerating during the deeper stages of NREM sleep
