There are 5 phrases of sleep: stage 1, 2, 3, 4 and REM (rapid eye movement). Stage 1 begins when you are sleeping, and subsequently go through each stage until reaching REM sleep, and then you begin the cycle again. Each complete sleep cycle takes from 90-110 minutes. The brain acts differently at each stage of sleep. In some of the stages, body may make movements, but arms and legs are immobile. Having good sleep habits will make sure each type of sleep are achieved.
Stage 1
Light sleep. Experience drifting in and out of sleep. Can be easily woken up. Eye movement and body movement slow down
Stage 2
Around 50% of sleeping time is spent on stage 2 sleep. Eye movement stops and brain waves (a measure of the activity level of the brain) become slower. There will also be brief bursts of rapid brain activity called sleep spindles.
Stage 3
First stage of deep sleep. During stage 3 sleep it can be very difficult to wake someone up. If woken up, may feel groggy and disoriented for several minutes.
Stage 4
Second stage of deep sleep. In this stage it is also very difficult to wake someone up. Both stages of deep sleep are important for feeling refreshed in the morning. If these stages are too short, may feel that you have not slept enough.
REM sleep - Rapid eye movement
The sleep stage in which dreaming occurs. This sleep phase begins about 70 to 90 minutes after you fall asleep. When you enter into REM sleep, your breathing becomes fast, irregular and shallow. Eyes will move rapidly and muscles become immobile. Heart rate and blood pressure increase.Source from next magazine
