Deep sleep phase: How sleep works


The body can regenerate best in the deep sleep phase. We explain what you should know about these and other sleep phases.
Why is the deep sleep phase so important for us?
If you can easily fall asleep and sleep through the night, you usually don't worry about whether your sleep is really restful - and therefore rarely think about the so-called deep sleep phase. Our sleep is only considered healthy if we go through all the so-called sleep phases several times during the night, reaching deep sleep and continuing for a certain period of time. Only in deep sleep can the body really regenerate and the brain process the impressions of the day.

Good sleep keeps us healthy
Healthy sleep helps our body to recover: Only those who sleep sufficiently ensure that body cells can renew themselves and that we remain physically and mentally fit. The problem: The process of sleep is extremely complex and susceptible to disturbances. There can be many different causes for sleep disorders, such as problems sleeping through the night. So anyone who has difficulty reaching and/or maintaining deep sleep must be prepared for a long search for possible triggers.

Deep sleep and Co.: The different sleep phases at a glance
There are different classifications of the sleep phases (also: sleep stages), depending on the model one assumes three, four, or five phases. Together they form a so-called sleep cycle, which should be passed through between four and six times per night to ensure that sleep is really restful. This corresponds to a night's rest of about eight hours. In the morning, after the last sleep phase, the so-called wake-up phase starts, after which we ideally start the day fit and awake. The sleep phases are classified as follows:

Falling asleep phase: The falling asleep phase rarely lasts more than 15 minutes for people without sleep problems and is often referred to as the "floating state" between waking and sleeping. During this phase the body becomes calm, pulse and breathing become more even and the muscles relax. If the person concerned sits upright, this can be seen, for example, when the head falls forward towards the chest in an uncontrolled manner.
Light sleep phase: The light sleep phase is also known as stable sleep. The muscles continue to relax, breathing, and heartbeat become calm. The light sleep phase usually lengthens with each individual sleep cycle. We usually spend most of our sleep in the light sleep phase - namely about half of the total sleep time.
Deep sleep phase: The so-called regenerative phase only begins with deep sleep: our body temperature drops to its lowest level, and blood pressure also drops. Pulse and respiration continue to slow down. In general, the body is completely relaxed and now begins to regenerate cells, i.e. it "repairs" itself. At the same time, the brain begins to process the events of the day. Furthermore, deep sleep strengthens the immune system, which makes us more resistant to viruses and bacteria. During the deep sleep phase, sleepwalking can also occur. In total, deep sleep accounts for about 20 percent of our total sleep time. In the first sleep cycle, it is about half an hour-long, the more cycles pass the shorter the deep sleep becomes.
REM sleep phase: REM sleep (REM = "Rapid Eye Movement") is also known as paradoxical sleep. The name of this sleep phase is because the eyes often move back and forth very quickly under closed eyelids during the REM phase. Our brain is extremely active during this sleep phase; in fact, its activity in some areas resembles the waking state. We dream intensely, can become sexually aroused in the REM phase, and the brain stores information in the long-term memory more easily. At the same time, our body is paralyzed - this is a protective function that prevents us from performing actions of the dream in reality. In contrast to deep sleep, the length of this dream phase increases with each sleep cycle: if it is initially only about five to ten minutes long, it often lasts 15 minutes or longer towards the end of the sleep period. In adults, this results in a total duration of about 75 minutes per night. By the way: newborns are almost exclusively in REM sheep. Experts assume that this is related to the development of the central nervous system.
Healthy sleep: What role does cell regeneration play 
In deep sleep, the body releases certain growth hormones that support the cells in their renewal. Only by renewing the cells regularly can our organs remain healthy for a long time and we can cope with the daily demands. If cell renewal is inhibited by a lack of deep sleep, for example, this can lead to serious symptoms such as persistent fatigue, irritability, and concentration problems.

Deep sleep is also important for learning.
It used to be assumed that the brain can only store information in the REM phase. However, this assumption is now considered obsolete: as early as 2014, researchers concluded in a study that deep sleep also plays a role, at least for learning new information (e.g. vocabulary). Those who have a healthy deep sleep could accordingly also have a better memory.

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