Sleep phases explained: This happens to your body at night

What phases are there and how do you influence the recovery of your body? In this article, you will learn everything you need to know – and it is easy to understand.

Everybody knows it. At some point in the evening we start to yawn and get tired. The bed is calling!

  • Our eyes become heavy and we gradually lose our focus.
  • These are signals that our body sends out to let us know that it is now time to go to bed.

Our sleep-wake rhythm is essentially controlled by our “internal clock”. The decisive factors for this include the change from day to night (or from light to dark).

Of course, the time since you last woke up also plays a role, but the sun controls the composition of hormones (the internal clock) significantly.

Our internal clock influences the body

Metabolic processes, behavior and growth performance are controlled by our “internal clock”.

Our daily rhythm is subject to the internal clock and many of us suffer from daily fluctuations.

For example, our digestion is throttled during sleep, because not so much energy has to be provided, or we experience a slack in the afternoon.

The normal rhythm of sleep is known as the circadian rhythm .

This rhythm can only be partially influenced – in the case of shift work or long-distance travel, for example, it is permanently disturbed.

You may have experienced the phenomenon as jet lag after a long flight .

How is my sleep actually induced?

In order to understand the phases of sleep, it is helpful to know how the body even knows that it is time to sleep.

The central nervous system (CNS for short) controls our sleep (just like many other processes in the body).

This is how the 1st phase of sleep begins

3 areas of our brain are particularly involved:

  1. The brain stem
  2. the thalamus
  3. and the hypothalamus

Note: Don’t worry if you’ve never heard of it. I’m just mentioning the brain areas for the sake of completeness. The next section can also be understood without a great deal of anatomy knowledge:

The brain stem sends the signals to sleep

Our brainstem is, so to speak, our “alarm clock” and ensures that we always wake up on time.

  • This sends out messenger substances (so-called neurotransmitters ) that cause irritation in the thalamus.
  • Conversely, the brain stem can also ensure that the activity of the thalamus decreases – we slowly get tired and fall asleep.

We can influence this natural process, but we can never stop it completely. As soon as we get tired, a lot gets going:

The signals affect our whole body

When the signals from the brain stem reach us, our muscles also relax.

That is why it is not too rare for us to tilt our head forward during a nap while sitting or to breathe with our mouth open while sleeping .

 

  • In addition to neurotransmitters, hormones also play an important role in maintaining a healthy circadian rhythm.
  • The sleep hormone melatonin is increasingly released in the evening, which means that the hypothalamus sends signals to the brain.

This means that we automatically know in the evening that it is time to sleep.

While sleeping

The central nervous system also controls all important processes in the further course of sleep.

The depth of sleep does not remain the same throughout, but rather varies in ever smaller intervals until the sleeper wakes up after about 6 – 8 hours.

This cycle is known as the sleep rhythm.

The different phases of sleep

In general, you can divide your sleep into 5 different stages.

You go through this night after night until we are in a deep sleep.

Using a special process ( electroencephalography , or EEG for short), scientists have managed to subdivide these phases too precisely by measuring brain waves.

In a sleep laboratory, experts can record when we are in which phase.

Stage I: The sleep phase

In the falling asleep phase we rest in a very light sleep. This stage represents the threshold between being awake and sleeping.

Our body slowly comes to rest and slows down our bodily functions – breathing slows down, the heart no longer beats as fast, the pulse drops and our muscles relax.

If you measure the brainwave activity using the EEG, you can see that the brainwaves are now slowing down.

Stage II: Light sleep

If we are in the second stage, we are in a light sleep.

This can be divided into two different phases:

  • The first phase is short and lasts a maximum of 10 minutes. Muscle relaxation subsides and involuntary muscle twitches occur.
  • In the second half of light sleep, the muscles relax again.

We are slowly moving into the third stage.

Stage III: The transition to deep sleep

This stage is seen as a transition phase to deep sleep. Muscle relaxation continues to decrease, breathing slows down. Our sleep continues to increase and we find it difficult to wake up.

Stage IV: The deep sleep

This is the deepest phase of sleep.

At this stage, phenomena such as speaking in sleep and sleepwalking occur because we can no longer consciously control our body.

Therefore, people who are woken up from it are often sleepy or disoriented.

Phases I-IV are called non-REM sleep in medicine, and muscle activity is steadily decreasing.

The REM sleep phase

After about 60 to 90 minutes, so-called REM sleep occurs. REM stands for “Rapid Eye Movement”.

  • As the name suggests, the eyes move back and forth very quickly during this phase. The brain is also very active during this phase.
  • The EEG waves are very similar to those of stage I, but there are violent movements of our eyeball at regular intervals.

Research has shown that people who are awakened from this phase can in most cases remember their dreams.

The dream phase also seems much more vivid and visual compared to the other phases.

Rigid sleep protects against injuries

During REM sleep, the muscles are completely relaxed (muscle atony).

  • The muscles are very relaxed and ensure that we “cannot live out our dreams”.
  • This is a protective mechanism to prevent our bodies from harming itself.

In this phase we do not change the sleeping position , but remain lying “petrified”.

However, other vital parameters are increased, such as blood pressure, breathing and heart rate or sweating during sleep (night sweats) .

The blood flow to the genital organs also increases (which in men often leads to an erection (the famous “morning latte”) with which he often wakes up in the morning).

We often go through the sleep phases several times

After we have lived through REM sleep, this sleep loop starts all over again.

  • We go through the above phases several times night after night and thus ensure that our brain can process what we have experienced on that day and our body recovers.
  • In the course of our sleep, the time span of our phases changes. At first, the deep sleep phase only lasts a few minutes, but then it gets longer and longer and can last up to an hour.

Calculate the sleep phases?

The “ideal” length of sleep is still controversial today. Scientists have been trying to figure this out for years.

  • For a long time, the focus was on the “negative” consequences of lack of sleep , but now the negative consequences of too much sleep are increasingly emerging.
  • According to studies from the USA, the “eight hours a day” we know are already too long for most (older) adults.

For many people about six to seven hours a day would be healthier.

According to studies from Regensburg, we Germans sleep about seven hours a day on average and still feel in top shape in the morning.

Individual differences influence the amount of sleep you need

Before jumping to conclusions, however, please keep one thing in mind: there are strong personal differences.

And the length of sleep also varies depending on the age. On average, adults sleep around 6-10 hours a day to be comfortable.

There are extreme differences, for example, in the age groups of infants and senior citizens.

  • Babies sleep most of the day (14-17 hours), but not in one piece, but spread out.
  • In the elderly, however, the need for sleep is much lower (senile bed escape).

In the following graphic you can see the differences again clearly summarized:

Are you sleeping long enough?

Do you belong to the group that needs more sleep than the average?

  • Then adjust your everyday life so that you can ensure the optimal amount of sleep for you.
  • If four to five hours a day are enough for you to be fit, then don’t force yourself to sleep longer!

This is important so that the body can carry out its regeneration processes without being permanently damaged by “wrong sleep training”.

Don’t fight your internal clock

Each person is an individual with special needs. It is important that you listen to your body and do not stick to fixed tables.

Whether the duration of sleep is sufficient is often related to the quality (and not just the number of hours).

For this reason, despite adequate bed rest, many people feel constantly tired – light sleep without deep sleep phases gives the body no opportunity for regeneration.

Note: Read this article to learn more about the optimal length of sleep .

Different day types

The performance is not constant within a 24-day rhythm, but is divided into minimum and maximum.

There are generally two types, depending on the person:

The morning person who is already full of energy and vitality in the morning, but whose ability to concentrate continues to decline towards evening.

In contrast, there is the night owl. He gets up sleepily and only starts doing things in the evening, since only then is his maximum performance achieved.

The body loves regular bedtime

It is worthwhile to look at your energy level from a distance and to optimally align your daily routine with it.

  • If you find it difficult to get out of bed in the morning, then it is often easier to “build” your own life around the needs of your body.
  • This is more promising in the long term than using stimulants to force the body into a rhythm that goes against the natural internal clock.

Whether you get up early or late: a healthy rhythm should be adhered to. Sleeping at the “wrong” time of day is relatively inefficient.

In short: stick to the naturally given circadian rhythm.

Why is sleep so important to us?

As mentioned earlier, sleep is essential.

Only then can our bodies regenerate in order to be able to maintain our life-sustaining processes.

  • For example, our brain can process the day’s experiences in peace. Without this mechanism, “hallucinations” and mental disorders can otherwise occur. By the way, things that we learn shortly before going to bed are best memorized.
  • Sleep is also very important for our defenses: while we sleep, the immune system works at full speed. It releases antibodies that help us fight diseases. A healthy sleep ensures that we do not get sick as often.

Those who do not get a healthy sleep in the long term can expect serious consequences.

Insufficient sleep – the lack of sleep and its consequences

If you don’t get enough sleep for a long time, your body will come forward.

Those affected often suffer from exhaustion, poor concentration, decreased productivity, impaired reactions, irritability and loss of energy.

Shrinking brain

In addition to the symptoms mentioned above, a study has shown that chronic sleep deprivation caused brain size to decrease in those affected.

This process is irreversible and leads to reduced performance. Complex tasks are made more difficult.

Faster skin aging

Not only our brains, but also our skin suffer from too little sleep. It ages faster, which is noticeable:

Our eyelids droop (“puffy eyes”) and form a dark border (“dark circles”), we look pale, wrinkles usually appear more quickly.

People around them tend to perceive people with sleep deprivation as “less attractive” and unhealthy.

Mental health problems – schizophrenia

After just 24 hours without sleep, it can happen that those affected develop symptoms that are similar to those of schizophrenia (hallucinations, changed body perception, loss of space and time).

Chronic lack of sleep also leads to the development of mental illness.

Causes of sleep disorders & wrong sleep phases

These problems with falling asleep make people sleep deprived:

To care

For example, worry makes it difficult to fall asleep.

If you are going through important changes, an exam is due, have received disturbing news or something similar.

Once you start thinking about things too much, the process of falling asleep is disrupted.

depressions

People suffering from depression also often have trouble sleeping.

They usually wake up too early or take a lot longer to fall asleep.

This can also be attributed to increased brain activity through too much thinking.

Diseases

Certain illnesses prevent us from getting a good night’s sleep.

For example with sleep apnea: Here, breathing stops briefly while sleeping. As a result, sleep is not as deep and those affected often wake up.

But sleep is also made more difficult in general with attacks of fever. Due to changing temperatures, the body does not properly enter the restful deep sleep phase.

Pain

Pain ensures that stimuli are passed on in the brain. This disrupts the normal rhythm, making it difficult to sleep.

Earache, throat pain, body aches, muscle aches, etc. keep you from getting a sound sleep.

alcohol

Alcohol makes you very tired, but you usually sleep less deeply and much more restlessly. This increases the likelihood of waking up earlier. It is therefore no wonder that you usually wake up “whacked”.

caffeine

Caffeine is a substance that makes us more alert and active.

  • It stimulates the nervous system, our heart and respiratory rates increase. But it also takes time for this substance to be processed by the body.
  • A cup of coffee in the evening can therefore often lead to problems falling asleep because your body is still “too active”.

It is best not to drink any caffeinated drinks after 5 p.m. in order to ensure a healthy sleep rhythm.

Disturbance of normal sleep patterns

People who work in shifts or who frequently travel back and forth between different time zones ( jet lag ) often have problems sleeping.

  • The disruption of the normal biological clock makes it difficult for the body to get to sleep.
  • The organism then needs a certain time to get used to the new rhythm.

However, some studies suggest that the body never gets completely used to it. For example, people who have moved to other time zones are at higher risk of suffering from many diseases.

Watch your internal clock and try to live with it – not against it.

Too much sleep is not healthy either

The Consequences of “Hypersomia”

Usually it is said: the more, the better. But not with sleep. People who sleep too long (hypersomia) usually wake up tired.

Often it is said, “I slept very tired”!

 

Research has shown that hypersomia poses an almost 50% increased risk of stroke and a 20% increased chance of dying earlier.

Too much sleep has also been shown to increase the incidence of the following diseases: diabetes, obesity, depression, Alzheimer’s and cardiovascular diseases.

Causes of “Too Much Sleep”

Often, the use of drugs or alcohol is a reason to sleep longer than you need to.

  • The consumption makes it easier to fall asleep, but the deep sleep phase is hardly reached and recovery does not take place.
  • Diseases like “sleep apnea” have the same effect. The deep sleep phase is hardly reached because you briefly stop breathing.

Even if you have slept for 12 hours without sufficiently reaching the deep sleep phase, the body cannot regenerate and you wake up “more tired than before”.

I have trouble sleeping – what should I do?

Recognizing sleep problems is the first step. Next, the cause must be found:

Do you drink coffee in the evening? Do you consume alcohol? Do you have a chronic illness?

Take a close look at your sleeping habits. I will go into this point in more detail below.

Going to the doctor can help

If you are not able to get your sleep disorders under control yourself, a visit to the doctor is inevitable.

  • They will analyze the situation and, if necessary, refer you to a sleep laboratory.
  • Sometimes the doctor will also prescribe sleeping pills. In any case, strictly follow the medical information.

Sleep problems can lead to serious health consequences. The early detection and action has a very positive effect on the following course of treatment.

Can I record my sleep rhythm myself?

In our modern age there are now methods that do not require a sleep laboratory to record our sleep.

For example, using fitness watches that are permanently worn on the wrist, the pulse and movement activity can be recorded.

The measurements can be evaluated using a special app and you can see at a glance whether you had a restful or restless sleep.

Note: Technology is always improving, but of course these measurements are not 100% accurate.

The sleep alarm clock

You can now buy special sleep alarm clocks in stores that recognize which sleep phase you are in. Depending on this, you will be gently woken up – often with an artificial sunrise, for example with these light alarm clocks .

These alarm clocks work in a similar way to the fitness watch and measure the sleep phases via the pulse and movement activity.

Soft vibrations on your wrist will wake you up and slowly wake you up from sleep.

Here’s how you can improve your sleep:

The first – and most important – step is to try to learn more about your sleeping habits.

In most cases it will quickly become clear which screws you need to turn.

 

Very few of us give much thought to our own night’s sleep – after all, we have already got used to routines that usually go back to childhood.

But since we spend a third of our life in bed, it is worth taking a closer look at your own sleep.

Note: You can find more tips with which you can significantly increase the quality of your sleep here: Sleep better .

Set up your bedroom optimally

One thing to start with today is furnishing your bedroom.

 

  • Is your pillow really comfortable, or do you wake up tense all the time?
  • Depending on the sleeping position, different variants (e.g. a side sleeper pillow) can be useful.

The right pillow or a suitable summer duvet is one of the cheapest ways to improve your sleep quickly and effectively.

Tip: You can find more information about the different variants and the best recommendations here: Pillow test .

Start with your personal sleep ritual

One of the best ways to get a good night’s sleep is with a daily routine

Each of these rituals can improve your sleep (and thus your entire life significantly). It’s best to pick one of these and get started today.

(Of course you can also develop several habits into your own personal sleep ritual – but for the beginning I recommend that you concentrate on 1 single thing).

You are also welcome to continue browsing through the sleep guides on this page – or the best way is to bookmark ( CTRL + D ) to come back here later.

I created Sleep Knowledge to share my interests and experiences on healthy sleeping with others. On this page I am therefore dealing with interesting questions about the optimal night’s sleep & everything else that goes with it.

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