Everything, everything, everything, you will know everything about sleep... Yes, well, the reference is dated (and probably a bit borderline), but fatigue has that effect on us! So, we're pretty well placed to talk to you about sleep, right?
More seriously, we are going to tackle the subject of sleep together with some juicy scientific data. REM sleep, deep sleep, rhythm and duration of sleep cycles… We explain everything in an article guaranteed 100% yawn-free!
Sleep: understanding the principles
So, what happens at night, when your eyelids are closed? Lots of little interesting things, because sleep time is far from a boring period! Indeed, during your sleep, several different phases will follow one another: these are sleep cycles.
Basic concepts
Before tackling the somewhat complex organization of sleep, let's review the basics: what is sleep, what are your needs and what are the effects of a lack of sleep on your body?
According to INSERM, sleep can be defined as “a lowering of the state of consciousness that separates two periods of wakefulness. It is characterized by a loss of vigilance, a decrease in muscle tone and partial preservation of sensory perception.”
In other words, when we sleep, we are less conscious, our body rests... but not necessarily our brain!
👉 It is actually during the night that it is supposedly most active, at different levels depending on the phases concerned.
Sleep and health
Getting a good night's sleep is an essential element for good general health. This is exactly what we explain in our great Instagram reel: why you need to sleep 😴!
If you're too lazy to watch (we caught you...), here is a quick summary of the benefits of a good night's sleep:
- 💤 fights fatigue (pretty logical)
- 🚮 toxin elimination
- 🙏 stress and mood regulation
- 🦠 improved immune defenses
- ♻️ contributes to cell renewal, especially in the nervous and muscular systems
- 🧠 memory and learning stimulation
- 🩸 blood sugar regulation (blood sugar levels)
- 🕵️ good level of alertness and concentration during the day
This list is not exhaustive, because a lack of sleep is also linked to the onset of certain disorders such as type 2 diabetes, obesity, high cholesterol, mood disorders, depression, learning and concentration difficulties... in short, you really should sleep!
Sleep needs
We are not all equal when it comes to sleep: some will need to sleep a lot each night, others less.
And age is one of the determining factors! Indeed, infants will have very different sleep needs than a child, adolescent, adult or senior.
- 👶 Babies need on average 14 to 17 hours of sleep per day,
- 🧒 Children and teens should sleep between 9 and 11 hours,
- 🧑 An adult needs 7 to 9 hours of sleep per night,
- 🧓 Seniors sleep on average between 6 and 8 hours
Depending on your age, sleep time varies and a quick reminder, screen time by age also does (and there is actually a link between the two, which we explain below 👇)
Sleep cycle: definition, composition and duration
Definition of the sleep cycle
A sleep cycle is a bit like the unit of measurement for your nights of sleep: it is the oscillation between the different phases of sleep. There are 4 to 6 cycles per night, each composed of 4 very different phases, each with a very specific purpose.
Duration of a sleep cycle
A sleep cycle lasts on average 90 minutes, with a composition that varies throughout the night. Specialists estimate that a good night's sleep includes between 3 and 5 successive sleep cycles.
Phases composing the cycles
Let's take stock of the different cycles that will pace your night...
Phase 0: Focus on falling asleep
Let's start at the beginning, what happens when falling asleep? This stage between wakefulness and sleep lasts on average 15 to 20 minutes and precedes the period when we are truly asleep. Our body gradually goes to rest, muscles relax, breathing slows down and we gradually sink into light sleep.
Several conditions are required to sink into the arms of Morpheus:
- 📉 Decrease in stimulation: the transition from wake mode to sleep mode is based on a 24-hour rhythm (the circadian rhythm which causes our sleep to synchronize with the day/night cycle). It is easy to understand why blue light can disrupt falling asleep by making the brain think it is still daytime!
- ↘ Neurotransmitters (a kind of messenger for our nervous system) linked to daytime activity decrease to prepare for falling asleep.
- ↗️ Melatonin production (the sleep and falling-asleep hormone) must be sufficient. However, it is decreased by the use of screens at bedtime. Indeed, blue light has a negative impact on melatonin production and therefore on falling asleep.
Once asleep, sleep cycles follow one another and break down into 3 true phases: we first enter light slow-wave sleep, then deep slow-wave sleep, we return to the light slow-wave sleep stage and then enter REM sleep.
Your nights are therefore far from a long, semi-quiet river!
Light slow-wave sleep
As the name suggests, when you are in light slow-wave sleep, you can be easily awakened. It is stage 1 of sleep (if we exclude falling asleep) where you can experience that oh-so-unpleasant feeling of falling into a bottomless pit.
This sensation of falling or even small muscle jerks are totally normal: it is the effect of muscles relaxing and preparing for phase 2.
So, there's no need to go to bed with climbing gear or to cling tightly to your pillow!
Note that this light slow-wave sleep is found at the beginning and end of each sleep cycle. It is a stage that should not be disturbed if you want to avoid waking up at night.
Deep slow-wave sleep
This is the calmest and deepest part (as the name suggests) of your nights. The body does not move and it is quite difficult to wake you up. And that's a good thing, because deep sleep is the most restorative. It is very present at the beginning of the night to ensure optimal recovery from the fatigue accumulated during the day.
Its role is therefore to allow you to recover but also to eliminate toxins, not to mention sorting through your memories of the day, contributing to cellular regeneration and helping the growth of the youngest through the secretion of growth hormone. It is not the soup that makes you grow, but indeed complete nights!
And it is so effective that if you are woken up in the middle of deep sleep, you will have trouble emerging! Similarly, if you spend a sleepless night playing Hogwarts Legacy, the following night your sleep rhythm will include more deep slow-wave sleep to recover.
This phase of slow-wave sleep ultimately constitutes only less than 2 hours accumulated over the entire night, at a rate of a few tens of minutes per cycle.
REM sleep
Its name comes from the in-between state in which your body finds itself: both deeply asleep with high brain activity.
It is the cycle where dreams occur, at least those we remember. We can observe an irregular pulse, movements of our eyes under our eyelids while the body is immobile (with the exception of a few jerks).
Things to know:
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During the night, the composition of sleep cycles evolves. The vast majority of the first part of your nights consists of deep slow-wave sleep, whereas afterwards, light slow-wave sleep and REM sleep dominate.
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If the duration of light slow-wave sleep and REM sleep varies from one person to another, that of deep slow-wave sleep is generally the same for everyone, whether a light or heavy sleeper!
Concrete example
At Horus X, we use the Oura Ring, a ring that allows you to analyze and optimize your sleep. We highly recommend it, by the way! Here is what a night of sleep looks like for Paul, one of our co-founders.
We can clearly see the different cycles (5 here) with variable durations. Much more deep sleep in the first phases, more REM sleep in the following ones.
Overall, your body spends the majority of the night in light sleep. The time you spend in REM or deep sleep can vary considerably from one person to another, but below you will find the averages you can expect for each stage during a single night.
- Wakefulness: 2 to 5%
- Light sleep: 45 to 55%
- Deep sleep: 13 to 23%
- REM sleep: 20 to 25%
How to improve your sleep?
If you haven't fallen asleep reading this article, you now know how important falling asleep and light slow-wave sleep are for quality sleep and why deep sleep is essential to your health.
And one of the points we would like to insist on is the harmful role of screens and blue light on your sleep. We often tell you, but blue light decreases the secretion of melatonin, the sleep and falling-asleep hormone, in addition to disrupting the circadian rhythm and causing headaches and other signs of digital eye strain.
So stop scrolling in bed! (and read a looooong file on sleep with blue-light blocking glasses, for example, that also works)
Final word: how long does a sleep cycle last?
Let's recap:
✅ Good sleep, in sufficient quantity according to your needs, is essential for good physical and mental health.
✅ A night of sleep is generally composed of 4 to 6 sleep cycles, lasting 90 minutes on average per cycle (more precisely between 1 and 2 hours).
✅ The sleep cycle itself breaks down into 3 phases: light slow-wave sleep, deep slow-wave sleep (the most restorative) and REM sleep.
✅ To improve the quality of your sleep and avoid sleep or falling-asleep disorders, avoid screens before going to bed!
