Sleep stages: what happens to us at night

Watching a baby sleeping peacefully, one might feel that not much is happening in our bodies while we sleep. But it is entirely different – ​​essential processes take place in our body during sleep.

These processes can be assigned to different sleep phases that our body goes through several times at night. A very rough distinction is made between REM sleep (REM=Rapid Eye Movement) and non-REM sleep, which can be subdivided into light sleep and deep sleep.

Different sleep phases

Depending on how long we sleep, our body goes through different phases around four to six times a night – a sleep cycle lasts around 90 minutes. The deep sleep phase is particularly long during the first sleep cycle, while the REM sleep phase is short. However, this changes throughout the night – the REM sleep phases continue to increase while the deep sleep phases decrease.

However, it needs to be clarified why our body goes through the individual sleep phases several times.

 

Non-REM sleep: falling asleep

The first stage of non-REM sleep, falling asleep, lasts only a few minutes for most people. It marks the transition from being awake to sleeping. The body relaxes, and the brain slowly comes to rest. You have fallen asleep if the brain is so relaxed that it no longer perceives external stimuli such as light touches or soft noises.

This first phase of sleep is often characterized by the feeling of falling or restless movements of the legs. The twitching of the legs is caused by the fact that the bodily functions are shut down at different speeds during sleep: while the brain is almost “asleep”, the muscles in the legs are still active. Stress can exacerbate muscle spasms when you fall asleep.

On the other hand, the feeling of falling is due to another phenomenon: lying in bed can lead to disturbances in the vestibular organ in the ear – these disturbances then result in the feeling that one is falling.

Light sleep: second phase of sleep

Falling asleep is followed by the light sleep stage. During this sleep phase, the body relaxes even further, breathing and heartbeat slow down.

The light sleep phase usually lasts between 30 and 60 minutes. Overall, it takes up more than 50 per cent of total sleep.

 

Non-REM sleep: The deep sleep phase

The deep sleep phase follows the light sleep phase. It is the most restful stage of sleep – during deep sleep, the body is motionless and completely relaxed. That’s why waking someone up from a low blow is very difficult.

In the deep sleep phase, many growth hormones are released. They also play an essential role in strengthening the immune system and regenerating cell tissue. In addition, deep sleep is also said to be of particular importance for learning.

The first deep sleep phase can last up to an hour; the further deep sleep phases during the night are shorter.

sleepwalking and talking in your sleep

Interestingly, sleepwalking or speaking during sleep occurs precisely in the deep sleep phase, in which the body is completely relaxed.

It is, therefore, assumed that sleepwalking is not – as is often assumed – the act of living out dreams because it is only during the REM sleep phase that we dream intensively.

After deep sleep, another light sleep phase before REM sleep begins.

The REM sleep

REM sleep is characterized by rapid movement of the eyes under closed lids. In this phase, the activities of our brain are similar to those of the waking state. Pulse and breathing also accelerate, and blood pressure rises.

As a result of this activation, the calorie consumption in this sleep phase is almost identical to that of the waking state. It is believed that most information processing occurs in the brain during REM sleep.

The REM sleep phase is also characterized by frequent dreaming. So that we don’t put our dreams directly into practice, the muscles in our body are paralyzed during this time. This fact results in the uneasy feeling everyone knows from their nightmares: you want to run away but can’t move.

 

Duration of the REM sleep phase

While the first REM sleep phase lasts only about ten minutes, the proportion of REM sleep increases overnight: In the early morning, the REM sleep phase can last up to an hour.

Overall, REM sleep accounts for just over 100 minutes per night of total sleep in adults. In newborn children, on the other hand, sleep consists almost exclusively of REM sleep phases. It is, therefore, assumed that they are of particular importance for the maturation of the central nervous system.