We all spend about one third of our life sleeping

Sleep may seem like one long state of unconsciousness, but sleep is actually made up of serveral distinct states. These states are split up into two general categories. REM or Rapid Eye Movement, and NREM or Non Rapid Eye Movement.

These to states occur in a roughly 90 minute cycle which is repeated 5 to 6 times a night. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep.

Dreams generally occur in the REM stage of sleep.

NREM or Non Rapid Eye Movement

Non-REM sleep is made up of four stages NREM1, NREM2, NREM3 and NREM4 that range from light dozing to deep sleep. Each stage can last from 5 to 15 minutes. A completed cycle of sleep consists of a progression from stages 1-4 before REM sleep is attained, then the cycle starts over again.

Our brain activity throughout these stages is gradually slowing down so that by deep sleep, we experiences nothing but delta brain waves.

During the deep stages of NREM sleep, the body repairs and regenerates tissues, builds bone and muscle, and appears to strenghen the immune system.

REM or Rapid Eye Movement

The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep.

The first period of REM typically lasts 10 minutes, with each recurring REM stage lengthening, and the final one may last up to an hour.

Most dreaming takes place during REM sleep. Periodic eyelid fluttering, muscle paralysis, and irregular breathing, body temperature, heart rate, and blood pressure distinguish REM from non-REM sleep stages.