Sleep cycle: what stages and how they work

The sleep cycle is a set of phases that start from the moment a person falls asleep and progress and become deeper and deeper until the body enters REM sleep.

Normally, REM sleep is the most difficult to achieve, but this is when the body can really relax and when the rate of brain renewal is highest. Most people follow the following pattern of sleep phases:

• Phase 1 light sleep;
• Phase 2 light sleep;
• Phase 3 deep sleep;
• Phase 2 light sleep;
• Phase 1 light sleep;
• REM sleep.

After being in the REM phase, the body goes back to phase 1 and repeats all the phases until it returns to the REM phase again. This cycle repeats itself throughout the night, but the time in REM sleep increases with each cycle.

How long does the sleep cycle last?

The body goes through several sleep cycles during the night. The first one lasts about 90 minutes and then increases in duration, up to an average of 100 minutes per cycle.

An adult usually gets between 4 to 5 sleep cycles a night, which ends up getting the 8 hours of sleep needed.

The 4 stages of sleep

Sleep can then be divided into 4 phases, which alternate:

1. Light sleep (Phase 1)

This is a fairly light sleep phase that lasts approximately 10 minutes. Phase 1 sleep begins the moment you close your eyes and the body starts falling asleep. However, it is still possible to wake up easily to whatever sounds happen in the bedroom, for example.

Some features of this phase include:

• Not realizing that you are already sleeping;
• Breathing becomes slower;
• It is possible to have the feeling that you are falling.

During this phase, the muscles are not yet relaxed, so the person still moves around in bed and may even open their eyes while trying to fall asleep.

2. Light sleep (Phase 2)

Stage 2 is the stage that almost everyone refers to when they say they are a light sleeper. It is a phase in which the body is already relaxed and asleep, but the mind is attentive and, therefore, the person can still wake up easily with someone moving in the room or with a noise in the house.

This phase lasts about 20 minutes and, in many people, is the phase in which the body spends the most time throughout all sleep cycles.

3. Deep sleep (Phase 3)

This is the phase of deep sleep in which the muscles completely relax. And the body becomes less sensitive to external stimuli such as movement or noise. At this stage, the mind is turned off and therefore there are no dreams either. However, this phase is very important for body repair. As the body is trying to recover from minor injuries that have arisen during the day.

4. REM Sleep (Phase 4)

REM sleep is the last phase of the sleep cycle, which lasts about 10 minutes and usually starts 90 minutes after you fall asleep. At this stage, the eyes move very quickly, the heart rate increases and dreams appear.

It is also at this stage that a sleep disorder known as sleepwalking can arise, in which the person can even get up and walk around the house, without ever waking up. The REM phase takes longer with each sleep cycle, reaching up to 20 or 30 minutes in duration.