The Sleep Circle

Non-REM Sleep
The period of non-REM sleep (NREM)is comprised of Stages 1-4 and lasts from 90 to 120 minutes, each stage lasting anywhere from 5 to 15 minutes. Surprisingly, however, Stages 2 and 3 repeat backwards before REM sleep is attained. So, a normal sleep cycle has this pattern: waking, stage 1, 2, 3, 4, 3, 2, REM. Usually, REM sleep occurs 90 minutes after sleep onset.

1. Drowsy Sleep
This is the time that you begin to sleep. The eyes are closed but if aroused from this state, a person may feel as if he or she has not slept. Drowsy sleep may last for five to 10 minutes.

2. Light Sleep
Stage two is a period of light sleep where muscle tone is mixed with periods of muscle relaxation. Muscles will tone as a reaction to auditory stimuli. At this point, the body prepares to enter deep sleep.

3. Deep Sleep

4. Intense Deep Sleep

Stages 3 & 4 are deep sleep stages, with Stage 4 being more intense than Stage 3. These stages are known as slow-wave, or delta, sleep.