What happens when we sleep?

Each year, we spend an average of 118 days sleeping. We do not necessarily realize it, but our body remains active even when we sleep. During the night, our temperature, breathing, brain, heart and muscle activity, and hormone production vary with each phase of sleep. Here are the 5 successive phases: falling asleep, light slow sleep, deep slow sleep, REM sleep and the awakening.


While falling asleep

Breathing becomes slower and the muscles relax. During this phase of semi-sleep, one can have the impression of zoning out or having spasms. The internal body temperature drops. When we fall asleep, the core temperature of our body will drop during the night to reach its lowest point between 4 and 6 am. Thus setting your room temperature around 19 ° C will give you the best sleeping condition. Melatonin is a fundamental hormone for regulating sleep and wake cycles. It is secreted when night falls and it is dark. Its production signals the brain that it is time to fall asleep. The secretion of melatonin will stop when the light around us increases. Blue light is therefore particularly effective in stopping the secretion process resulting in trouble falling asleep. This is why you should avoid looking at screens (television, smartphone, tablet, etc.) before going to bed. The ideal is to put in place a digital curfew at least an hour before going to sleep.

During light slow sleep

The electrical activity of the brain slows down. The muscles relax more and the breathing becomes calmer. However, during this phase, sleep is shallow and fragile: the slightest external stimulus, a noise or a change in light, can cause us to wake up from our sleep.Also, the level of cortisol, a hormone that helps the body to cope with physical or psychological stress, decreases, which, in return helps you fall asleep. 

During slow deep sleep

Breathing is very slow and regular. The heart rate slows down and the muscles are totally relaxed. And when the heart rate drops, blood pressure also drops and is at its lowest level. Brain activity is slowed down, however, it is during this phase that the connection between neurons is most optimal, which helps to boost memorization and creativity, for example.  

During REM sleep

The body is totally inert and paralyzed. On the other hand, brain activity is at its peak and under our closed eyelids, the eyes make rapid movements in all directions. This is why this phase is also called "rapid eye movement sleep". It is during this phase that we dream the most. During REM sleep, our brain demonstrates high electrical as if we are awake or barely asleep. However, from a behavioural point of view, we sleep soundly and our muscles are paralyzed. We simultaneously exhibit signs of deep sleep and signs of wakefulness.

While waking up

The temperature of the body increases gradually, which will stimulate the awakening process. This is why it is recommended in the morning to wake up to take a rather hot shower to keep the muscles relaxed and to do some stretches to warm up the body faster. Cortisol is secreted between 6 and 8 a.m. Cortisol is stimulating and promotes awakening. The melatonin level, on the contrary, is at its lowest.