What are the stages of sleep?

There are five phases of sleep: stages 1, 2, 3, 4 and REM (rapid eye movement).

Stage 1
Stage 1 sleep is light sleep. You experience a drifting in and out of sleep. You can be easily woken up. Your eye movement and body movements slow down. You may experience sudden jerky movement of your legs or other muscles. These are known as hypnicmyoclonia or myoclonic jerks. These “sleep starts” can give a sensation of falling. They are caused by the motor areas of the brain being spontaneously stimulated.

Stage 2
Around 50 percent of your time sleeping is spent in stage 2 sleep. During this stage, eye movement stops and your 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
Stage 3 is the first stage of deep sleep. The brain waves are a combination of slow waves, known as delta waves, combined with faster waves.
During stage 3 sleep it can be very difficult to wake someone up. If you are woken up during this stage, you may feel groggy and disoriented for several minutes.

Stage 4
Stage 4 sleep is the second stage of deep sleep. In this stage the brain is making the slow delta waves almost exclusively. 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, sleep will not feel satisfying.

REM Sleep – Rapid Eye Movement
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 and your muscles become immobile. Heart rate and blood pressure increase. Men may develop erections. About 20 percent of sleep is REM sleep for adults.

REM sleep is also the phase of sleep in which you dream. 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.
Researchers do not fully understand REM sleep and dreaming. They know it is important in the creation of long-term memories. If a person’s REM sleep is disrupted, the next sleep cycle does not follow the normal order, but often goes directly to REM sleep until the previous night’s lost REM time is made up.