What are the stages of sleep? There are two general states of sleep: (1) rapid eye movement (REM) sleep, and (2) non-rapid eye movement (NREM) sleep. 

REM sleep is unlike any of the other stages of sleep. In REM sleep, brain waves have a fast frequency and low voltage, similar to the brain waves seen in the normal awake state. Other characteristics of REM sleep include complete inactivity of the voluntary muscles in the body, with the exception of the muscles that control eye movements. Rapid eye movements are also observed during REM sleep. People who are awakened during REM sleep often report that they were dreaming at the time. About 20 per cent to 25 per cent of sleep time is REM sleep; in infants it can comprise about 40 per cent.

NREM sleep has traditionally been divided into four stages. However, new guidelines from the American Academy of Sleep Medicine (AASM) have re-characterised NREM sleep as occurring in three stages, according to the pattern of brain electrical activity.  About 80 per cent of sleep is NREM sleep. If you sleep 7-8 hours a night, all but maybe an hour and a half is spent in dreamless NREM sleep. Sleep typically occurs in cycles that range from 90 to 120 minutes in length, with 4-5 cycles occurring during each night's sleep.

In the first half of the night, there is a transition from wakefulness into stage one NREM sleep, then to stages NREM two and three. Stages NREM two and three then reappear followed by the first instance of REM sleep. Cycles of stage NREM two and REM sleep alternate with each other for the second half of the night.

Read on next week as we will provide you tips on choosing the right mattress for you, so you can get the most comfortable, rejuvenating night’s sleep!