There are 4 stages of Non-Rapid Eye Movement (NREM) sleep and 1 stage of Rapid Eye Movement (REM) sleep. NREM sleep makes up about 75% of the sleep cycle, while REM sleep makes up the remaining 25%.
Stage 1 is the transition to sleep, stage 2 is when breathing and heart rate slow down, and stages 3 and 4 are deep sleep stages where the body repairs itself.
REM sleep is when dreaming occurs, and the brain is highly active. During this stage, your eyes move rapidly, your breathing becomes irregular, and your muscles become paralyzed.
The sleep cycle typically lasts around 90 minutes, and people go through multiple cycles each night!