Sleep cycles are the natural patterns of sleep that occur throughout the night. Each cycle typically lasts about 90 minutes and consists of different stages, including NREM (non-rapid eye movement) and REM (rapid eye movement) sleep. During these cycles, the body goes through various processes, such as physical restoration and memory consolidation. A typical night of sleep includes several cycles, usually ranging from four to six. In the first half of the night, NREM sleep dominates, while REM sleep becomes more prominent in the later cycles. Understanding sleep cycles can help improve sleep quality and overall health.