Sleep is the state of natural rest and is necessary for survival. Nearly a third of our life is spent asleep. Infants spend most of the day asleep and as we grow older sleep becomes lighter and more interrupted. There are 3 important phases of sleep that make up a normal night of sleep. These are:
- Quiet sleep or non-rapid eye movement (NREM) sleep
During this period the body is active and the brain inactive, and there is relatively little dreaming. It is believed that NREM sleep is the time of growth and rejuvenation of the immune, nervous, muscular and skeletal systems.
- Deep sleep or slow-wave sleep
Longer periods of slow wave sleep occur in the first part of the night. Children and young adults will have more total slow wave sleep in a night than older adults. The elderly may not go into slow wave sleep at all during many nights of sleep. This is the period of sleep when sleep walking can occur.
- Rapid eye movement (REM) sleep
In REM sleep, the brain is active and the body inactive, and this is when most dreaming occurs.
As we age we have less deep sleep and less REM sleep and this can affect the quality of sleep.