Sleeping is the most natural thing in the world—after all, we all do it every night. But what sounds simple is actually a complex process consisting of multiple cycles and phases. Let's be honest: How much do you actually know about what happens in your body at night?
Table of contents
1. The four phases of sleep
Not all sleep is created equal—that would be too simple. In fact, somnology, or sleep research, has been puzzling over what exactly happens in our bodies and brains when we close our eyes at night for centuries. Many questions continue to puzzle researchers. What everyone agrees on, however, is the fact that we go through different sleep phases night after night—multiple times in succession.
These phases are roughly divided into REM sleep and non-REM sleep. REM stands for "rapid eye movement" and refers to the sleep phase in which we typically dream. The other three phases are referred to as non-REM sleep. These are also the phases we go through first when we fall asleep in the evening – in this order:
Stage #1: Falling asleep
The onset of sleep phase is the first phase we go through during nighttime sleep. It represents the transition between the waking state and the deeper stages of sleep later in the night. During the onset of sleep phase, our body winds down, and our brain activity decreases. Darkness triggers the release of our natural sleep hormone melatonin, which reduces energy consumption and body temperature, signaling to our body that it's time to rest. This process can take between 5 and 30 minutes. Our sleep is still very light at this stage; noises or other disturbances can quickly wake us up again.
Stage #2: Light sleep phase
During the light sleep phase, our brain activity decreases even further, and our heart rate and breathing slow down. Our body enters rest mode, and as a result, our body temperature also drops. During this phase, our brain begins to process the experiences of the previous day. However, we are still in a rather superficial state of sleep, meaning it is easy to wake us up again.
Stage #3: Deep sleep phase
The deep sleep phase is crucial for the regeneration of both our bodies and our brains. Previously, this sleep stage was further divided into a medium-deep and a very deep sleep phase, but researchers now combine both phases under Stage 3. The deep sleep phase is also called slow-wave sleep because the particularly slow delta waves characteristic of this stage are evident in the EEG during this phase.
During the deep sleep phase, our heart and breathing rates reach their lowest points, blood pressure drops, and our muscles relax. Our bodies also release the growth hormone HGH (Human Growth Hormone) – researchers believe this is an important factor in our body's nightly regeneration. Eye movements do not occur during this phase, but teeth grinding, sleep talking, or even sleepwalking may occur. As we age, the amount of time we spend in deep sleep at night decreases. This also explains why our physical and cognitive functions gradually decline as we age, and our performance is reduced.
Stage #4: REM phase (dream sleep)
During the REM phase, our brain processes the events of the day. Although dreams also occur during other sleep phases, this is by far the phase when we dream most and most intensely. This is when the typical rapid eye movements occur, which give the REM phase its name. While we are in REM sleep, our breathing rate increases, our heart rate accelerates, and we may occasionally experience muscle twitches. Furthermore, during this phase, our sleep is more shallow, and noises can easily wake us.
2. One night – several sleep cycles
The first REM phase of the night is usually followed by a light sleep phase—we go through all sleep phases several times per night. Sleep researchers therefore refer to sleep cycles, each lasting approximately 90 to 110 minutes. We repeat these cycles an average of five to seven times per night.
The first sleep cycle at the beginning of the night is characterized by the fact that the deep sleep phase is extremely long relative to the other phases (up to an hour), while the REM phase is rather short (approximately 10 minutes). With each subsequent cycle we go through during the night, this relationship gradually reverses: In the final sleep cycle, the dream phase predominates, while we spend hardly any time in the deep sleep phase. This also explains why we often wake up from a dream in the morning.
3. Sleeping well made easy
If we go through the various sleep cycles at night without major disruptions, we usually wake up the next morning feeling refreshed. Waking up from time to time during the transition from one phase to the next is normal and doesn't disrupt our healthy sleep rhythm. We usually fall asleep again immediately and can't even remember being awake the next morning.
However, if we lie awake for a long time at night or have difficulty falling asleep, we speak of sleep disorders. If you suffer from sleep problems, it is important to maintain strict sleep hygiene: You should only go to bed to sleep. You should also darken your bedroom and ensure there are no disturbing noises. If worries or anxieties keep you awake, you can encourage the process of falling asleep and thus accelerate the transition into the deep sleep phase, for example, with relaxation exercises or gentle sleep aids like the SLEEP SPRAY with natural melatonin . You can find more tips on how to support your healthy sleep rhythm here .
Circadian lighting can also help improve your sleep quality. It is based on the human biological rhythm, often referred to as the body clock, to dynamically adjust color temperature and brightness throughout the day. This way, your body always receives the right lighting conditions, regardless of the season or weather, even if you spend most of your time indoors. The effect of this type of lighting can be measured using digital sleep trackers and other devices. The most important indicator, however, is whether you wake up refreshed from your night's sleep.
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4. Conclusion
According to a study, many Germans sleep an average of less than seven hours a night – far too little, according to scientists. This isn't surprising, however, because people who enjoy sleeping a lot are often labeled as lazy. But the opposite is true: Those who make their sleep a priority aren't lazy, but rather masters of self-care! And we should all take a leaf out of their book. Because sleep is wellness for body and soul.
