four stages of sleep that we cycle through several times each night. The first three form the so-called non-rapid eye movement (REM) sleep and the fourth one is REM sleep — where dreams occur.In the first non-REM stage, the body and brain transition from wakefulness to sleep.
The brain changes its electrical oscillations from the active, wakefulness pattern of brainwaves into a slower rhythm. Muscle tone throughout the body relaxes.
This is the phase during which our bodies may twitch as we enter slumber. The second non-REM stage involves a drop in the body’s temperature, the heartbeat and breathing become slower, and the brainwaves slow down further.