Sleep cycle: what phases and how they work

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

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

Light phase 1 sleep; Light phase 2 sleep; Deep phase 3 sleep; Light phase 2 sleep; Light phase 1 sleep; REM sleep.

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

Know the 8 main disorders that can affect the sleep cycle.

How long the sleep cycle lasts

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

An adult usually has between 4 and 5 sleep cycles per night, which ends up getting the necessary 8 hours of sleep.

The 4 stages of sleep

Sleep can then be divided into 4 phases, which are intercalated:

1. Light sleep (Phase 1)

This is a very light sleep phase that lasts approximately 10 minutes. Phase 1 of sleep begins the moment you close your eyes and the body starts falling asleep, however, it is still possible to wake up easily with any sound that happens in the room, 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 is still moving around in bed and may even open their eyes while trying to fall asleep.

2. Light sleep (Phase 2)

Phase 2 is the phase that almost everyone refers to when they say they are light sleepers. 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 inside 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 relax completely, the body is less sensitive to external stimuli, such as movement or noise. At this stage the mind is disconnected and, therefore, there are no dreams either. However, this phase is very important for body repair, as the body tries to recover from small injuries that have been appearing 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 falling 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.

Learn more about sleepwalking and 5 other strange things that can happen during sleep.