The sleep cycle is a concept that everyone is familiar with. REM sleep, deep sleep... You're probably familiar with these terms, or have heard them before. However, it's important to look into the subject, as it can help you improve your sleep! To know how to sleep, the ideal is to have a good understanding of how sleep works. Let's dive into the complex structure of sleep!
How is sleep organized?
Sleep isn't a straight line: between going to bed and waking up, we go through several stages of sleep. These are called "sleep cycles."
Sleep consists of a succession of these phases. Generally, 4 to 6 cycles occur during the night. Each cycle has three main phases: light slow-wave sleep, deep slow-wave sleep, and REM sleep, also known as rapid eye movement sleep.
During a cycle, phases of falling asleep, then light slow-wave sleep, follow one another, leading to deep slow-wave sleep. At the end of the cycle, after a return to light slow-wave sleep, a phase of REM sleep appears.
How long is a cycle?
A cycle lasts about 90 minutes on average, and there are generally 3 to 6 cycles per night. However, this remains an average; sleep varies from person to person.
The first half of sleep contains mostly deep slow-wave sleep phases, while the second half of sleep is rich in light slow-wave sleep phases and REM sleep phases.
Sleep tends to change with age: older people tend to have fewer phases of deep slow-wave sleep.
Falling asleep
The falling asleep phase corresponds to the first stage of sleep. It marks the transition between wakefulness and sleep. During this phase, breathing slows down and muscles relax. During this phase of sleep, it is common to feel like you are falling through a void, or to experience jolts. There is nothing to worry about; these sensations are perfectly normal and common.
This phase generally lasts between 5 and 20 minutes. Beyond this time, especially after 30 minutes, it may be due to insomnia; it is then advisable to speak to a doctor.
Slow-wave sleep
During slow-wave sleep, the brain's electrical activity is significantly reduced: normally, in a calm state, the brain reaches an electrical frequency of 8 to 12 hertz. When asleep, the brain has very low electrical activity, which can drop to 1 hertz in deep slow-wave sleep.
Light slow wave sleep
This phase follows the falling asleep phase. Sleep is not very deep, and it is easy to wake you up with the slightest noise or sufficient light.
This phase represents 50% of total sleep.
Deep slow-wave sleep
The deep slow-wave sleep phase is a phase where we are deeply asleep. The heart and breathing follow a regular rhythm, and the body does not move. This is a phase in which it is difficult to wake up, where the brain becomes increasingly insensitive to external stimuli (lights, noises).
This is the time of sleep when we recover the most from accumulated fatigue. The entire body is at rest and recovering. It represents about a quarter, 20 to 25%, of sleep time, and occurs particularly early in the night.
REM sleep
The REM sleep phase is the most well-known because it's when we dream the most. Its name comes from the word "paradox," which refers to the conflict between the signs of deep sleep (still, completely relaxed body) and the signs of wakefulness (eye movements, intense brain activity, which are caused by dreams). Heart rate may also increase, as may breathing. However, this depends on what we're dreaming about.
This phase represents approximately 20% of total sleep time.Â
Which phase is the most restorative?
The deep sleep phase is the most restorative phase for the body. During this phase, the body recovers much of its accumulated fatigue.
In which phase do we dream the most?
We dream throughout the night, but especially during the REM sleep phase. It is during this phase that dreams are most abundant and vivid.
