Sleep stages: why they're key to feeling properly rested

What happens when we sleep?

Sleep is by no means a state of total rest. When we're asleep, we do things like switch our body position, change our facial expressions, flicker our eyelids, snore and change our breathing rhythm. In addition, we can wake up to twenty times per night without being consciously aware of it.

Not all sleep is the same

WConsequently, while we sleep, our body isn't in the same state all the time. Functions such as our pulse, breathing rate and brain activity change, which all affect our sleep pattern.

Based on brain wave activity, muscle tension and eye movement, experts have divided sleep into different sleep phases. While we sleep, we pass through each phase four to five times in one night.

How many different stages of sleep are there?

Our sleep cycles basically consist of five stages. In the course of a night, we constantly switch from one stage to the next. Sleep diaries can help us to identify medical conditions. People suffering from depression, for example, have a different sleep pattern: the deep sleep stages tend to be shorter.

Falling asleep (stage 1)

When we go to bed, and slowly begin to nod off, we are in the falling asleep stage. In this transition phase between being awake and asleep the body’s muscles begin to relax.

Light sleep (stage 2)

After some time, contact to the surroundings gradually decreases and our muscles relax all the more. Any muscle twitching takes place during this stage, the transition to the deep sleep phase.

Deep sleep (stages 3 & 4)

In the following deep sleep phase, our heart and circulation activity is reduced to a minimum. Blood pressure and body temperature drop as the body slowly switches to "standby". Because of the slow brain waves, this sleep phase is also called slow-wave sleep. At the same time, it may happen that we sleepwalk or talk during this sleep phase. The deep sleep phases are mainly longer in the first half of the night, and can last up to an hour. If we are suddenly woken from this sleep phase by some external factor we often feel somewhat disoriented and confused.

REM sleep (stage 5)

This sleep phase is sometimes also referred to as "paradoxical" sleep. This is because the waking threshold during this phase is very high, even though our brain is highly active. Our muscles are completely relaxed at this moment. This is key, because it is in this sleep phase that we dream. Because our muscles are inactive, we can't perform our movements in the dream. However, if we awaken during this phase, we can remember the content of our dream particularly well.

Apart from some muscle twitching, the rapid eye movements are the only muscle movements during this sleep phase. This is why this stage is also called REM sleep, which stands for "rapid eye movement". It is believed that REM sleep plays an important role in processing experiences and storing them in our long-term memory. After the REM phase, a new sleep cycle begins again.

Sleep diaries can help us to identify medical conditions. People suffering from depression, for example, have a different sleep pattern: the deep sleep stages tend to be shorter, and the REM stages occur sooner. An easy way to track how you sleep? The sensors on smartwatch bracelets can produce simple sleep diaries.

Sleep phases influence regeneration and learning

Each of these stages of sleep is important, as each has its own purpose and fulfils an important function in the body. When we sleep, we pass through several cycles of these phases. This means that anyone suffering from disturbed sleep patterns or depression will find that their condition doesn't just affect how long they sleep, but that their sleep stages change too. Here are examples of how these sleep phases affect us:

• Feeling rested: if the deep sleep phases are shortened, the body has a hard time regenerating.
• Learning: waking up during REM sleep interferes with the learning processes that take place while we are asleep.
  

If we sleep too little or wake up several times a night, the sleep phases cannot fulfil their functions.