How Sleep Functions Across Cycles and REM and Non-REM Phases

Jun 11, 2025

Those who have trouble falling and staying asleep often focus on the duration of sleep. While this is an important factor, it is just one element in defining sleep quality. Another major consideration is whether sleep is restorative and involves the four distinct stages that make up the sleep cycle. During a good night’s sleep, one progresses through these stages multiple times as they work cumulatively to restore the mind and body and ensure that one wakes up refreshed.

In addition to stages, there are two phases: rapid eye movement (REM) and non-rapid eye movement (NREM). The first three stages of each cycle of sleep (N1 through N3) are NREM. The final stage of the cycle is REM, and this repeats across however many sleep cycles one has across the night.