The 5 stages of sleep and their importance

According to research, healthy sleepers under the age of 30 spend about 2 hours per night in deep sleep. Over 65-year-olds, on the other hand, only get deep sleep for 30 minutes. If you've had enough deep sleep, you'll wake up feeling rested and fully productive. A lack of deep sleep is likely whenever you didn't feel physically or mentally fit in the morning. The deep sleep phases only occur in the first sleep cycles of the night. Therefore, you should not go to bed too late and ensure that you sleep as undisturbed as possible. The 1st deep sleep phase is the one that lasts the longest and gives the most recovery. In the second half of the night there are no more deep sleep phases.What is the REM sleep phase?

Sleep – the source of mental fitness, creativity and a good mood. It's no secret that you should get enough sleep. But not only the length of sleep is crucial so that you can start the next day full of energy. It is also important that the sleep cycles at night run as undisturbed as possible. A sleep cycle comprises the unique sequence of 5 sleep stages. What happens in each sleep stage? Why is being awake also part of sleeping? And what is REM sleep?

Why sleep is so important

Even if many people would like to give up sleep in order to get more done. It's not a habit, it's absolutely essential. Because when we sleep we recover physically and mentally. While we sleep, our consciousness has a break, but our body works at full speed. Now he starts with important repair work and renewal processes. New cells form, the body detoxifies more intensively, the immune system recovers and fights off potential invaders such as pathogens.

Growth hormones are also released during sleep, which make babies and small children grow. They bring relaxation to the cells of adults. The brain processes the sensory impressions of the day and classifies the experiences into the world of experience. Newly learned information is transferred from short-term memory to long-term memory and stored.

If you sleep less than 7.5 hours or suffer from insomnia, your body cannot finish its nightly tasks and is therefore less regenerated. You can feel this very clearly the next day, for example when your concentration, creativity or your memory are limited. Your mood is also affected by a lack of sleep. You feel less motivated, maybe even sickly or depressed.

What are the sleep stages?

Sleep doctors have found that we sleep according to a fixed pattern. We go through a fixed sleep cycle 4 to 6 times per night. This always consists of the same sequence of different sleep stages and lasts on average around 90 minutes. The individual sleep phases can be clearly distinguished from one another based on different brain activities. Sleep physicians divide our sleep time into:

  • the waking state
  • the falling asleep phase (non-REM sleep)
  • light sleep (non-REM sleep)
  • deep sleep (non-REM sleep)
  • REM sleep (dream sleep)

Characteristics and importance of the individual sleep phases

Sleep phase 1 in the sleep cycle: the waking state

Sleep physicians also count the waking state before falling asleep and during the night as part of healthy sleep. Because whether you remember it the next day or not: You wake up several times during the night, even if only for a few seconds. But since wakefulness cycles in the same way as the other phases of sleep, it is counted as sleep time. According to research, we emerge from our nocturnal unconsciousness 10 to 30 times. However, since this waking state usually lasts less than 1 minute, we forget about waking up again until the next morning. The time was simply too short to save the experience.

When you lie down in bed and your consciousness is still wide awake, the first phase of sleep begins. During this time you are still thinking about the events of the day and gradually find yourself in a calmer and more relaxed state. The waking state accounts for around 5% of the total sleep time.

Sleep phase 2 in the sleep cycle: the falling asleep phase

The falling asleep and light sleep phase or (Non-REM N1) together last about 50 minutes. In the falling asleep phase you look for a suitable sleeping position and you are still present with your consciousness in the real world. Thoughts of the day are still present in your head. But you gradually slip from being awake to asleep. Dozing is typical for the falling asleep phase. You gradually detach yourself from the here and now. You decouple your consciousness from real things. Your muscles relax. Your brain comes to rest. At times during this sleep stage you feel like you are falling. This moment brings you back to consciousness for a moment. Slowly your ideas become more dreamlike, less realistic. Nevertheless, in this sleep stage you can still be awakened very quickly by a disturbance such as a noise.

Sleep phase 3 in the sleep cycle: light sleep

Light sleep is also known as stable sleep or non-REM sleep N2. We spend about half of our total sleep time in this sleep phase. It lasts about 20 minutes per sleep cycle. In the EEG (electroencephalography) you can see similarly pronounced brain wave patterns as in the sleep phase. But they can also be less pronounced – as in deep sleep. Then the brain is already significantly less active even during light sleep.

Your muscles relax even more when you sleep lightly. Sometimes, in this stage of sleep, you involuntarily flinch. The eyeballs only move slowly behind the closed eyelids (Slow Eye Movement, SEM: "slow eye movements"). Your sleep becomes increasingly deeper and the first dreams can arise. It is characteristic of the dreams in the light phase that they still have a very strong connection to reality. Here we often process real problems that are on our minds.

K complexes and sleep spindles

It is typical of light sleep that so-called K-complexes become visible in the EEG. These particular waveforms appear when the brain perceives environmental stimuli, such as a sound or bright light, during sleep. "K" stands for the first letter of the English word "knock", which means "to knock". In a figurative sense, an external stimulus knocks on our consciousness door and wants to be let in. So that you do not wake up from such external stimuli, the body has developed a protective mechanism that can be seen in the EEG as so-called sleep spindles. In this phenomenon, several definable brain waves occur in a typical sequence. Sleep spindles appear on the EEG whenever something has disturbed our sleep and we should not wake up.

Sleep phase 4 in the sleep cycle: deep sleep

The deep sleep phase (Non-REM N3) accounts for about 15% of total sleep. A deep sleep phase lasts an average of 30 minutes. This sleep stage is longest at around 1 hour when it first occurs during the night and gets shorter and shorter in the subsequent cycles. Deep sleep gives the body the recovery it needs to be physically and mentally productive the following day. At this stage, regenerative processes such as cell renewal take place.

Absolute relaxation in deep sleep

Now our body is completely relaxed. The muscles are completely relaxed, blood pressure, heart rate and respiratory rate drop to a minimum. We breathe deeply and calmly. Eye movements hardly take place. The level of cortisol, our stress hormone, is lower than in any other phase of sleep. The brain is also on the back burner. This can be clearly seen from the wave patterns in the EEG. At this stage there is a slow frequency of brain waves with large swings

Sleepwalking and teeth grinding in deep sleep

During deep sleep, we also anchor what we have learned in long-term memory so that we can recall it at a later point in time. If you tend to sleepwalk or grind your teeth, now is your time. Because these phenomena occur in deep sleep. If your body is disturbed during deep sleep, it will be difficult for you to wake up. You then have great problems finding your way back into the here and now.

Sleep stage 5 in the sleep cycle: REM sleep

Brain more active in REM sleep

REM sleep is the 5th phase of sleep. In this phase, the focus is primarily on mental recovery. A REM sleep episode always follows a deep sleep phase and marks the end of a sleep cycle. REM stands for Rapid Eye Movement. Because the characteristic of this sleep stage is that the eyes move violently under the closed eyelids. This already indicates that our brain is more active again during this sleep period - comparable to the waking phase or the falling asleep stage. The brainwaves pick up speed again with an increased frequency. Energy consumption, blood pressure and heart rate are also reminiscent of a person who is awake.

In REM sleep, our dreams are intense

It is no wonder that brain activity increases again during the REM sleep phase. Because in REM sleep you dream a lot - and often very intensely. In contrast to the other sleep phases, in which we can also dream, the dreams in REM sleep are no longer abstract, but have a real plot - like in a movie. In addition, they are emotionally charged and often filled with fear or panic. Often in such nightmares you will be followed, hurt or experience other bad things. Fortunately, nature has arranged it in such a way that you cannot move during this sleep phase. Because your motor center is in standby mode for the time being. This prevents you from trying to escape, stimulated by a vivid dream, and trying to climb down the stairs, for example.

According to sleep researchers, 60 to 70% of our dreams tend to be negative, with only 30 to 40% being positive. From this they conclude that when we sleep we mainly process the negative sensory impressions of the day. Thanks to sleep research, we also know that we construct our dreams. They don't run as a continuous film, as we often believe. Rather, they are composed of various fragments to form a large whole. A dream usually lasts no longer than 20 minutes.

Lucid dreaming in REM sleep

In addition to beautiful dreams and nightmares, there is lucid dreaming. "Lucid" derives from the Latin word "lux" which means "light". Lucid dreaming describes the occurrence of dreams in which, while dreaming, you become aware that you are dreaming. In these dreams you can actively determine the action from the moment you become aware by making decisions yourself. Best of all, you can learn this lucid dreaming skill. With the help of certain techniques you will learn to control your dreams at will. One such technique is waking mindfulness meditation. However, electronic aids or other substances can also be used. With the electronic aids, stimuli are generated from the outside by means of sensors, which the dreaming notices in the dream and becomes aware of dreaming during sleep.

REM sleep varies in duration throughout the night

At the beginning of the night, in the first sleep cycles, only short REM phases occur. We spend a lot of time in deep sleep and light sleep. For example, the first REM episode only lasts a maximum of 10 minutes. Towards the end of the night, when the deep sleep episodes become shorter, the REM sleep phases take up more space. If you wake up during this sleep period in the sleep cycle, you usually have a good memory of your dream.

REM sleep important for emotional balance

REM sleep is important for our emotional state, among other things. At this stage, your brain processes the emotions so that you can be balanced again the next day. For example, if you don't get enough REM sleep, you suffer more from mood swings. On the other hand, if you spend too much time in this sleep phase, you are more prone to depression than if you get enough REM sleep.

REM sleep important for learning

If you don't get enough REM sleep, you'll be less efficient and focused the following day. In addition, you are slower in thinking, but all the faster in forgetting.

Why the undisturbed flow of the sleep phases is so important

For mental and physical fitness on the following day, it is not only important that you get enough sleep, but also that your sleep cycles are undisturbed. This has been established in various studies. Your physical and mental performance suffers if you wake up during a deep sleep phase, for example. Because then the cycle that has started is aborted and starts again from the beginning. If this happens more frequently at night, the light sleep phases take up a lot of space, while the deep sleep and REM phases necessary for regeneration lose time. The result: your sleep is less restful.

Sleep phases in babies

Babies go through the same sleep cycle as adults. However, they sleep more, but in shorter stages. This applies to both day and night. They also wake up from sleep more often than adults. Unlike adults, REM sleep precedes deep sleep in the baby's sleep cycle. The deep sleep phase is then followed by another shallow sleep phase before waking up briefly and then gradually sinking back into deep sleep. A baby's sleep cycle lasts about 50 minutes and is repeated 3 or 4 times in many newborns. Then follows a longer waking period. Some babies are already rested after 1 or 2 sleep cycles and don't want to sleep anymore.

REM sleep in babies

REM sleep occurs relatively frequently in babies because it is particularly important for the development of the brain, for example for the development of motor memory. Since babies and toddlers learn a lot of new things every day, especially in relation to movements (learning to walk, cycling, etc.), extended REM sleep phases are important. Older people, on the other hand, no longer have to learn so many new things. You can already run and bike. Therefore, they no longer need such extensive REM sleep phases.

The REM sleep phase in babies, like in adults, can also be recognized by the rapidly moving eyes under the lids. In addition, there are often twitches, the so-called "angel's smile" or brief crying during sleep. In this sleep phase, the baby is very easy to wake up. It should therefore not be lifted up or disturbed in any other way during this time. If a baby wakes up during this phase, it is no longer so easy for him to go back to sleep. Mothers should therefore only put their baby from their arms to the bed when this sleep phase is over and deep sleep has begun. A mother recognizes the baby's deep sleep when the newborn's body and arms are very heavy. In deep sleep, the baby hardly moves his eyes. It breathes deeply, calmly and regularly. A newborn baby in a deep sleep cannot be disturbed by disturbing stimuli. If there is a loud noise, for example, it simply goes back to sleep.

sleep phases in old age

Sleep phases change with age. The deep sleep phases become shorter as we get older. In women, the proportion of deep sleep in total sleep is only around 10% at some point. According to studies, this downward trend continues unabated in men. Older people often no longer reach the deep sleep stage. The REM sleep phases also take up less space in older people. The recovery that these two stages of sleep give the body is missing in old age. That's why they like to make up for the missed night's sleep in the form of short naps during the day.

Measuring sleep phases - making it easier to wake up?

There are various devices on the market today to record and measure your sleep phases. In addition to the popular fitness bracelets, there are apps for smartphones and sleep phase alarm clocks that you can use to bring light into the darkness of your sleep.

Measure sleep phases with the fitness bracelet

To determine when you are in which sleep phase, you can use a modern fitness bracelet with a corresponding additional function. An integrated sensor measures heart rate and movement activity during sleep. To wake up rested, you can be woken up by an alarm clock integrated in the fitness bracelet during a light sleep phase. To do this, you set a time span on the device in which you are able to get up instead of a fixed time. This way you can avoid an alarm clock waking you up in the middle of a restful deep sleep. This is how you should be able to start the day more rested with the help of a fitness bracelet.

Measure sleep phases with the sleep phase alarm clock

You can also determine your sleep phases with a special bedside alarm clock in combination with a bracelet. A sensor in the bracelet also measures your bodily functions such as pulse and breathing rate during the night. The respective sleep phases are calculated from this. You can also enter a time span for waking up the sleep phase alarm clock. If the sleep phase alarm clock measures a moment during which you are sleeping very superficially, it sounds an alarm. However, if the device does not notice a light sleep moment, the alarm sounds at the end of the set time window. It is gently awakened by slight vibrations on the wrist.

Measure sleep phases using a smartphone app

Smartphones also offer the function of a sleep phase alarm clock. You can use a corresponding app to measure your breathing rate, body temperature and heart rate during the night. The different sleep phases are then determined from this. If the moment is favorable and sleep is superficial, you can use this app to gently bring you back from the dream world to reality via the wake-up function.

Measuring sleep phases using EEG in the sleep laboratory


In a sleep laboratory, the individual sleep phases can be measured in an EEG (electroencephalogram). The device uses electrodes to record the brain waves. Based on the wave pattern, sleep physicians can then recognize which sleep phase you were in at a certain point in time. The sleep laboratory measurement is the most accurate of all methods. The REM phases in particular can be captured well by an EEG. Bracelets and apps do this less precisely. However, sleep monitoring in the sleep laboratory is complex and is therefore only used after all other available methods for investigating the causes of sleep problems.

frequently asked Questions

What is a sleep cycle?

A sleep cycle is a passage in the sequence of the sleep stages light sleep, deep sleep and REM sleep. We go through 4 to 6 such sleep cycles every night. At the beginning of the night, the deep sleep phases are dominant, towards the end of the night there is more REM sleep.

What is the REM sleep phase?

REM sleep is particularly important for mental regeneration. In this sleep phase, the eyes move quickly behind the closed lids. REM stands for Rapid Eye Movement, which means "rapid eye movements". During this sleep phase, we dream particularly intensely. In it, we mainly process the negative experiences and emotions of the day.

How long should deep sleep be?

According to research, healthy sleepers under the age of 30 spend about 2 hours per night in deep sleep. Over 65-year-olds, on the other hand, only get deep sleep for 30 minutes. If you've had enough deep sleep, you'll wake up feeling rested and fully productive. A lack of deep sleep is likely whenever you didn't feel physically or mentally fit in the morning. The deep sleep phases only occur in the first sleep cycles of the night. Therefore, you should not go to bed too late and ensure that you sleep as undisturbed as possible. The 1st deep sleep phase is the one that lasts the longest and gives the most recovery. In the second half of the night there are no more deep sleep phases.

Why are sleep disorders so dangerous for health?

According to the World Health Organization (WHO), sleep disorders represent one of the greatest health risks. Because of them, the stages of sleep cannot take their usual course. The undisturbed succession of light sleep, deep sleep and REM sleep (1 cycle) and then REM sleep, deep sleep, light sleep in reverse is essential for the regeneration of body and psyche. If there are faults during a cycle, the cycle is aborted and starts again from the beginning. As a result, you get too little deep sleep overall, so that the body is not sufficiently recovered after the night.

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