Sleep Disorders Center
Stage 1 is the transition stage between being awake and being asleep. For a person not suffering from a sleep disorder, this stage can take about one to five minutes to occur.
Stage 2 is a period of light sleep. The body's heart rate and temperature decreases. At this stage of sleep, the body prepares to enter a deep sleep.
Stages 3 and 4 are deeper stages of sleep. Stage 4 is more of an intense sleep than stage 3. These stages are known as slow-wave, or delta, sleep.
Stage 5 is called REM sleep. This stage is distinguishable from the previous stages of sleep because it is characterized by rapid eye movements. During REM sleep, the body's heart rate and respiration speed up and become erratic, while the face, fingers and legs may slightly twitch. Intense dreaming occurs during this stage of sleep. This is the final stage of the sleep cycle and can last anywhere from ten minutes to an hour.