Sleep is a fascinating phenomenon that has been studied by science for decades.
There are five stages of sleep. Stages 1 – 4 are classified as ‘non rapid eye movement’ sleep or NREM. Phase 5 is ‘rapid eye movement’ sleep or REM. In most cases the person sleeping begins in stage 1 and continue through to REM, at which point the cycle begins again. Each complete cycle takes between 90 – 110 minutes.
Stage 1 is light sleep. Eye and body movement slows down but, you can be easily woken.
Stage 2 begins after 5-10 minutes. During this stage eye movement stops, and your brain waves become slower. Your muscles alternate between relaxing and contracting; the heart rate slows and body temperature decreases. Around 50 percent of your time sleeping is spent in stage 2 sleep.
Stages 3 and 4 of sleep are deep sleep. During these stages the brain is making slow waves; however in stage 3 these are combined with faster waves. In stage 4 the brain is almost exclusively producing slow delta waves. In both these stages it can be very difficult to wake a person up. Deep sleep is very important for feeling refreshed. If these stages are too short, then sleep will not feel satisfying.
Stage 5 (also know as REM sleep) is the sleep stage, in which dreaming occurs. When you enter into REM sleep, your breathing becomes fast, irregular and shallow; your eyes will move rapidly; heart rate and blood pressure will increase and your muscles will become immobile. (Except in the case of Narcolepsy). For adults, about 20 percent of sleep is REM sleep. This sleep phase begins about 70 to 90 minutes after you fall asleep. The first sleep cycle has a shorter phase of REM sleep. Toward morning, the time spent in REM sleep increases, and the deep sleep stages decrease.
REM sleep is known to be important to brain’s ability to construct long-term memories; it is also essential to the body. Interestingly, if REM sleep is disrupted, the next sleep cycle often progresses directly to REM sleep, until the previous night’s lost REM time is made up.