Sleep Cycles: How They Work and How Long Should You Sleep

Sleep has a lot to say and it's a super interesting process. It goes through several important stages so that you can have a deep and restful sleep. Find out what they are here.


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You thought it was just falling into a deep sleep and that was it, didn't you? Well, you're wrong, it's much more than that!

Your biological clock or circadian cycle is the one that controls all this! In addition to sleep, it also regulates blood pressure, appetite, alertness, body temperature and hormone levels.

The word “circadian” means “about a day”, which is why the circadian cycle is associated with an internal clock, with several hands: hormone levels, body temperature, metabolism and sleep. 

As a clock, the body synchronizes and adapts to various external factors.

The organism will thus react to the movement of the hands of the clock and to light. That's why shift workers have a harder time staying awake at night and sleeping during the day.


The Sleep Pressure

 But it's not just the fact that there is a clock inside our brain that makes us fall asleep. We also sleep through the action of a balancing mechanism called sleep pressure. What is it, you ask? 

Very briefly, it's our brain's need for sleep. It's similar to the urge to eat when you're hungry. 

When you wake up in the morning, this pressure is almost zero, however, as the day progresses, the sleep pressure increases progressively, reaching its maximum value at night, when you need to sleep. As soon as you fall asleep, your sleep pressure returns to values very close to zero again.

If, in the middle of the day, you feel like taking a nap longer than 20 minutes, the sleep pressure will decrease dramatically at that point and then there is no time to go back to the higher values that make you fall asleep at night. That's why the ideal nap last a maximum of 20 minutes.

But there is also another important thing! When you sleep little, the possibility of microsleep increases. 

In these small sleeps, we fall asleep involuntarily, for a very brief period (less than 3 seconds) without being aware of them or being able to control them. 

These episodes can have disastrous consequences, such as causing car accidents. That's why it's important to take rest breaks in longer trips.


What is a Sleep Cycle?

Our body and our brain work in perfect harmony so that you can fall asleep, sleep and remain in this wonderful state of rest for several hours. But how does all this happen?

Well, before we explore all the stages/stages of sleep, it's essential to first understand what sleep cycles are all about.

Although sleep duration is important for good rest and for a well-regulated circadian/clock cycle, sleep stages are also a subject worth exploring.

The sleep cycle is the phases our body goes through during sleep. There are, therefore, 4 stages of sleep, each with a specific duration.

Not all sleep cycles are the same length as they vary depending on factors such as sleep patterns, age and preferences.

During sleep, the body goes through these different phases several times: about 4 to 6 times.

These stages of sleep consist of two processes:


It means rapid eye movement. This is what happens:

  • The consolidation of memories of the facts and episodes we have lived through 
  • Processing our emotional memories
  • The movement of our eyes under the eyelids, while the body is paralyzed
  • The acceleration of breathing and brain activity, which is very similar to what we have when we are awake

REM sleep is very important for your health, as it is at this stage that there is great brain activity. It is when several hormones essential for your body are produced and are retained new learnings. Therefore, it is essential that sleep is not interrupted until you reach this stage.

This sleep phase is the most difficult to reach, as it is the deepest stage of sleep, where the body is finally able to relax. The stages that occur before this one belong to NREM sleep.


It means non-rapid eye movement, and is opposite to REM. Its phases are:

  • Shallow sleep: change from normal state to sleep
  • Deep sleep: Resting and restorative functions

As sleep progresses, there are fewer NREM phases, increasing REM sleep episodes.


What are the stages of sleep?

As we have already seen, there are 4 stages of sleep: in one of them there is rapid eye movement (REM sleep), and the other three correspond to non-REM sleep (NREM). 

Each of the sleep phases/stages is determined by brain activity while you sleep. They have different patterns, and this is what makes it possible to identify them:


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Normally, our sleep routine goes through these phases, always in the same order:

  1. Light Sleep Stage 1
  2. Light Sleep Stage 2
  3. Deep Sleep Stage 3
  4. Light Sleep Stage 2
  5. Light Sleep Stage 1
  6. REM Stage 4


After REM sleep, the body goes back to phase 1 and repeats the whole sequence, until it returns to phase 4 again. This cycle is repeated throughout the night, so the time in REM sleep increases with each cycle .

Adults can typically have 4 or 5 periods of REM sleep throughout the night. At the beginning of sleep, these moments are shorter, but at the end, they can be longer. Adding these sleep periods together gives approximately 90 to 120 minutes of REM sleep per night. Amazing, isn't it?

But now, let's explore each one in more detail:

Phase 1

It's the transition phase. In it, we have not yet fully relaxed the body. This is where the brain starts to slow down, altering its activity. Then the body starts to relax even more.

Here we still move around in bed, being able to open our eyes several times as we try to fall sleep.

Some features of this phase are:

  • Breathing becomes slower
  • We don't realize that we are already asleep
  • It feels like we're "falling"

Phase 2

When we enter this phase, our muscles completely relax and our breathing slows down, as does our heart rate. 

Body temperature drops and eye movements stop, entering NREM sleep. Here it becomes more difficult to wake up because of external stimuli.

Phase 3

In this stage the body completely relaxes and recovers from the day we had.

This phase is extremely important, as it is here that our immune system is strengthened, as well as the bodily functions essential for survival.

Progressively, it gets shorter as the night goes on, as you are about to reach REM sleep.

Phase 4

And that's it, we're in REM sleep!

It is at this stage of sleep that our brain activity increases and some physical changes take place, such as rapid eye movements, increased heart rate and breathing.

It is in REM sleep that dreams begin!

During this phase, another curious thing also happens: the atony.

Atony is the temporary paralysis of all but the respiratory and eye muscles. Act like a protection against ourselves.

Imagine you are having a nightmare where you are violent with yourself. This paralysis protects you from getting hurt in real life. Your body won't want to wake up with bruises or scratches for sure!

However, if you have a sleep disorder such as sleep-walking, in which you can exit the mattress and walking around the house even while sleeping, it is in REM sleep that it will happen.


👀 Disorders associated with REM sleep 

For some people, REM sleep may not be synonymous with deep sleep, because it could be a sleep disorder that disturbs rest.

In general, this disturbance is called REM sleep behavior disorder, characterized by violent reactions to dreams.

Those who suffer from this problem may have several involuntary movements, as if they were really living what they dream of. 

For example, when we are dreaming that we are going to fall, we often “jump” in bed. Has it ever happened to you?

In many cases, one can also scream, speak loudly, laugh or even cry.

It is, therefore, a manifestation that is still being studied by the scientific community. So, if this happens to you, don't worry, it really happens very often!


What is the ideal sleep time for me?

Falling asleep and waking up at the same time and having a sleep routine It is very important for your body to understand what are the ideal times to rest and to wake up. 

In this way, the stages of sleep will take place in a correct and complete way, so that sleep is deep and restorative instead of being a focus of instability.

If you don't follow a proper sleep routine, you will disrupt your circadian cycle/biological clock, and your sleep will become inverted (changing day for night).

You will be much more likely to wake up many times during your rest, interrupting your sleep cycle, affecting the quality of rest and compromising your health in the long run.

If you work through the night and can't sleep, it's even more important that you stick to your sleep routine on a daily basis. This is one of the best sources of production of melatonin.

In addition to regulating sleep, melatonin will also regenerate cells exposed to stress, pollution and other elements that can harm our body. Therefore, it is extremely important that you have and maintain a good sleep routine.


Does age influence sleep hours?

Knowing how long we should sleep depends a lot on our age. As a rule, as she progresses, we need less sleep.

The total time of REM decreases with age, that is, the younger you are, the more REM sleep you have. That's why a baby has to sleep more than an elderly person. 

However, there is one interesting thing you should know about the influence of your age on the most important stage of sleep - REM sleep:

A newborn, for example, sleeps more than 80% of its sleep in the REM phase because it needs the most assimilation in the world. An elderly person, who does not need to retain so much information, has only 10% of his sleep at this stage. Curious, right? There's really a lot to tell you!

But that doesn't mean you shouldn't give your body all the rest it deserves. You must respect it and pay the greatest attention to it, because the truth is this: the body is in charge… and age too!

If you read us, you already know well which consequences that the sleepless nights can have. So, it's important that you follow our advice, because when your head doesn't have any sense, we already know who pays, don't we? The body.

So that all doubts disappear, here is a very simple table that can change your perspective:


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The amount of sleep increases if we are sleep deprived. Getting too little sleep creates a sleep debt that needs to be minimized to keep one's body functioning properly.

For most adults, 7 to 9 hours a night seems to be the ideal amount of sleep, although there are people who need just five hours and others who need ten hours of sleep a day.

Important! If you are a woman in the first three months of pregnancy, you will always need several extra hours of sleep. And that's perfectly normal, it's still okay!



While it's important to keep these recommendations in mind, you shouldn't feel trapped by them. Each person is different.

You may even feel more rested with extra hours of sleep, or even discover that, for example, 7 hours is what your body needs to feel refreshed.

What matters is your sleep needs and how that makes you feel good and rested.

1 comment

  • Muito útil! Parabéns pelo excelente trabalho e informação prestada.

    Paulo D’Ávila

    Paulo D'Ávila

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