Sleep Cycle Specifics and Effects

Sleep is essential for a healthy body and brain development. However, having suffered from insomnia at a young age, I can clearly understand the problems and challenges of those having sleep-related issues. My insomnia situation compelled me to study medicine and, eventually, venture into therapy.

Through years, I have gained vast experience in sleep disorders treatment, and it has led me to blog writing to help those having insomnia and other sleep-related problems. I aim at helping you to understand the different sleep cycles, what happens during each stage, and the effects these phases have on your body during the daytime.

I have to agree that despite that sleep is one of the most intuitive things to human beings, many people still don’t know much about its nature. So, I want to start with the basics of sleep. What is the sleeping cycle? What are the stages of sleep? What are the phases’ separating factors? Read on to find out the answers to these questions.

Understanding the Stages of Sleep

A sleep cycle is a progression between non-rapid eye movements to rapid eye movement sleep in a re-occurring process. Technologies allowed us to create a sleep cycle alarm clock. Such a device can awaken people at the light stage of sleep, thus, resulting in natural waking up.

So, how many stages of sleep are there? Well, science knows four or five stages, depending on the terms used. Some researchers consider being awake as one of the sleep cycle stages, thus, adding to the initial classification. Nevertheless, to those wondering, what are the 5 stages of sleep, here’s a list of the phases:

  • Wakefulness – W
  • Relaxed wakefulness – N1
  • Light sleep – N2
  • Deep sleep – N3
  • Dreaming – Rapid eye movement (REM) sleep

Further stage subdivision considers rapid eye movement and non-rapid one. Steps N1 to N3 are referred to as non-rapid eye movement sleep (N-REM). The principal determiner of each stage is physiological change, making the phases challenging to understand.

So, how long is a sleep cycle? It takes anywhere between 90-110 minutes. An 8-hour sleep is most likely to guarantee you the full sleep cycle.

In this article, I will evaluate 4 stages of sleep, the ones except for wakefulness. The information below will help you to know what happens during a given stage, the features of every period, and the ideal role of each level. I have described all the processes in detail so that you could find out the features of every stage, understand their characteristics, and stages of sleep chart. That said, let’s get started.

Relaxed Wakefulness – N1

This stage acts as a link between being awake and falling into the deeper sleep phases. It is also the easiest stage to wake up from. It is the illogical thought phase as you drift towards deep sleep. However, you have a clear understanding of your surroundings, although it will change as you fall into deeper stages.

The phase is the shortest one and takes up to 5% of the total sleep. For every eight hours of sleep, the N1 stage translates into 24 minutes of sleep. However, many people spend less than ten minutes in the N1 stage. Here’s a summary of what happens during this phase:

Physiological features of N1:

  • The primary body temperature begins to drop.
  • It is a stage of N-REM or slow eye movements.
  • There are no sleep spindles here.

What do you feel during this stage? 

  • You gradually lose your surrounding awareness.
  • Illogical thought begins.
  • Hypnic jerks.

The stage’s purpose is to offer a link between being awake and falling into a deep sleep.

Light Sleep – N2 – The Spindle Occurrence Stage

Girl sleeping on the bed under the colourful blanket

Sleep during this stage is light and regenerating. It makes waking up easy. Likewise, there’s a relaxation in the upper airway muscle that impacts your breathing. That’s why it is possible to note that someone is asleep even without apparent signs of it.

The change in the breathing sounds serves enough to tell that a person has fallen asleep. The N2 phase covers a considerable portion of the total sleep, as it makes up from 45% to 50% in young adults. This equates to 3.5 to 4 hours of every 8-hour sleep. Below is a list of the stage’s features:

Physiology of N2 stage: 

  • K-complexes and spindles are present.
  • The heart rate is decreased.
  • Blood pressure is reduced.
  • No eye movement.


The purpose of the N2 stage is to offer a resting and recuperating platform.

N3 – The Deepest Stage of Sleep

The deep sleep phase is essential for cell renewal. The stage is also known as slow-wave sleep. During this period, neurotoxins and other wastes are removed from the brain. The stage differs from the rest, as waking up from it is extremely hard. Having woken up after this phase makes you feel somewhat disoriented.

The stage involves muscle activity, and that’s how people can move during the phase. It explains the experience of a night terror, bedwetting, sleepwalking, and talking during the N3 stage.

Besides that, the phase involves growth hormone release, as it is essential in restoring the stressed muscles. The stage also provides a chance for immune system restoration and brain refreshment for a new day ahead.

The ideal sleep quality depends on all the other stages, even though this one is the most crucial. It is advisable to practice suitable sleep hygiene measures and boost your deep sleep occurrence through acts such as taking hot showers before sleep.

That said, the stage is associated with slow large amp delta waves. The quality of N3 sleep changes with age, as adults frequently wake up at night, and it decreases deep sleep quantity.

Physiology of N3 sleep:

  • Slow and large amplitude delta waves.
  • The growth hormone is released.
  • No eye movement.
  • Blood pressure and heart rate decrease.


  • Difficulty in waking up.
  • The feeling of disorientation when awoken from the stage.


  • Waste removal from the brain.
  • Cell repair and renewal.
  • Glycogen restocking.
  • Long-term memory work.

Brief Information About REM Sleep Cycle

The REM stage is known as the rapid eye movement phase. At this time, the body is “paralyzed” while the brain runs in dreams and thoughts. Throughout all this period, the eyes are moving rapidly under closed lids. During the rapid eye movement sleep stage:

  • The body temperature rises, and the body loses its temperature regulation ability.
  • Heart rate rises.
  • Rapid eye jerking is observed.
  • Blood pressure increases.
  • Limb muscles become paralyzed.
  • Males experience arousals.
  • Breathing speeds up, thus, becoming shallow and irregular.

Most of the listed features match daytime levels during the REM stage. The phase sees the peak activity of the “fight-or-flight response” that rises twice compared to its daytime alertness. However, all these acts take place without body movements. All muscles, other than the essential breathing and eye movement ones, are steady and relaxed.

For those wondering, “What stage of sleep do you dream?”, the REM phase is the answer. It can be further explained by high brain activity while the body is “paralyzed.” That said, let’s look at when the REM stage takes place.

When Does REM Sleep Take Place – Sleeping Cycle Calculator

Normal sleep takes about six to eight hours for adults. As stated earlier, this period can be described as two halves. The first one consists of mainly N2 and N3 sleep cycle stages with minimal N1 and REM sleep. As you drift towards the night, the quantity of deep sleep and N3 begins to decrease. The other two stages, N1 and N2, remain the same.

The second half can be considered as the period of increasing REM stages of sleep. One may experience between three to five REM sleeps during the entire rest. It translates to a REM period after every 90 minutes. The longest one of such periods happens before a person wakes up.

When woken up in the process, you may find yourself struggling with sleep in the next few minutes or hours. This heightened sleepiness sensation is referred to as sleep inertia. After stages of sleep deprivation and with the beginning of undisturbed sleep periods, the REM sleep sets in early and lasts longer, and is also known as REM rebound.

Role of Rapid Eye Movement Sleep

With the period when the stage occurs in mind, I find it essential to help you to understand the benefits associated with this phase. Similar to deep sleep, the REM period is vital for mind restoration. Researchers believe that this stage is utterly crucial when it comes to clearing out irrelevant information from your brain.

Likewise, this period helps in learning and memory enhancing. After taking tests on people who had experienced good night’s sleep, many of them had considerable improvements in their retention score on the new tasks they had learned. However, those who were frequently awoken from REM sleep lost their gains.

In contrast, the participants who were awoken from the deep sleep stage had their improvement scores unaffected. This research can be used to explain why students who prepare for exams overnight may fail to retain much of the content as compared to those who slept well. Sleep cycle alarm may work best when set to awake you after deep REM sleep.

What Happens with a Person at Each Stage of Sleep

Young woman sleeping and seeing nightmares

Dreams occur at the REM stage. Humans dream for a total of two hours that are consequently divided into sleep cycles. Dreams happen even when you can’t remember what the thought was all about. During the dreaming stages of sleep, the pons, the brain part where REM signals originate, shuts off the spinal cord signals.

It makes your body remaining still during the dreaming period. The state is utterly crucial, as it prevents people from acting whatever they are dreaming about. It also helps to prevent injuries of falls or walking because such acts would happen without senses inputs. However, some people suffer from a rare REM sleep disorder that results in sleepwalking.

That said, the pons is likewise responsible for sending signals to the cerebral cortex that ensures information relaying and processing. The brain parts that get aroused during the REM sleep are vital for learning and memory saving.

Infants spend up to 50% of their sleep in the REM stage as compared to the 20% spent by adults. That’s why a high rate of learning is associated with a tender age.

How Does the Sleep Cycle Change with Age – Sleeping Cycles Calculator

Sleep is not constant throughout one’s life. There are lots of factors that lead to alteration in the quality and quantity of sleep. But first, let’s take a look at how age affects this condition. The following five growth stage have an impact on your sleep:

  • Newborns – up to 4 months old 

Newborns lack distinctive sleep waves, thus, no sleep cycle calc can give you accurate results. Their sleep can be categorized as active, quiet, and indeterminate. Newborns spend most of their time in active sleep, which is similar to the REM stage. However, there’s a slight alteration to quiet (N-REM) sleep. During active rest, it is quite easy to wake up, and it reflects a newborn’s frequent awakenings that complement their feeding habits.

  • Infants – between 4 months to 1 year 

Infants start experiencing regular distinctive sleep waves that result in scheduled sleep patterns. They sleep between 10 to 13 hours of every 24 hours, and this time includes 2 to 3 naps during a day.

  • Toddlers– between 1 to 3 years 

The average sleep at this age is 9.5 to 10.5 hours of every 24 hours. Toddlers have developed distinctive sleeping waves, and they mainly experience the urge for at least one daytime nap. It occurs mostly in the afternoon and serves as the ideal preparation for good night sleep.

That said, according to the toddlers’ sleep cycle calculator, they spend up to 25% of their sleep in the N3 stage. The stage’s approximate duration is similar to one spent in the REM phase.

  • Preschool – between 3 to 6 years 

The sleep pattern at this age isn’t much different from the one experienced by toddlers. It is about 9-10 hours of 24 hours. For many children, afternoon naps are essential between 3 to 4 years. During this period, the N3 stage is relatively long as compared to the other phases.

  • School-age – between 6 to 12 years

Sleep doesn’t change much here. The school-age sleep cycles calculator shows that the N3 stage takes from 20% to 25% of the sleeping time with 9 to 10 hours of sleep a day. It is the period of growth and development, and, thus, highly important for children.

  • Adolescent – over 12 years of age 

Adolescents sleep from 9 to 9.5 hours. The occurrence of physiological changes in the circadian rhythm alters the sleep cycle. These changes make adolescents wanting to sleep later and extend their morning naps. As age progresses, the cycle gets restored, and an average adult sleeps 5 to 8 hours for every 24 hours.

Factors Affecting Sleep Quality and Quantity

After a comprehensive look at the age specifics, it is vital to know the other determinants of the ideal sleep stages. The information below will help you to learn what things to avoid for healthy sleep and optimal relaxation.


During REM sleep, the body’s ability to regulate temperature is low. Thus, sleep can be disrupted as a result of a considerable room temperature change. Bear in mind, the difference doesn’t necessarily need to be a reduction in degrees, as hot temperatures will, likewise, result in sleep disruption.


Drugs are known either REM or deep sleep suppressors. For instance, whereas beer or wine may be considered as a fast route to relax, sleep quality after drugs is considerably lowered.

Previous Night Sleep

A need for quality sleep depends on how well you slept last night. Quality sleep, likewise, depends on your brain activity. High brain metabolism will similarly result in a dire need for sleep.

If you have been deprived of sleep for the previous days, it is possible to see a rebound on your next sleep after deprivation. That said, circadian rhythms, as well as sleep disorders, play an integral part in sleep cycle alteration.

Frequently Asked Questions on Stages of Sleep Cycle

Now, I want to take you through the mainly asked questions about the stages of sleep. The answers below will help you to understand the different stages of sleep and the specifics of each phase.

Sleep spindles are brief bursts of high-frequency brain waves and are deemed essential for learning and memory. They mainly occur during the N2, or light sleep, stage. The main purpose of this phase is resting and recuperating.

Night terrors can occur during the N-REM sleep stage. They cause great fear while sleeping and can last between 3 seconds to 3 minutes. Night terrors can result even in shouts or screams of people experiencing nightmares. Such conditions are most common among children.

However, night terrors can still occur at a later age, and they are often accompanied by sleepwalking. On the bright side, nightmares’ impact can be considerably reduced through the use of some proven techniques and proper rest. Below are the symptoms of a night terror:

  • Heavy breathing and a racing pulse.
  • Screaming and shouting.
  • Dilated pupils.
  • Limbs thrashing.

Sleepwalking is common during the deep stage of the N-REM sleep. It mainly happens after the night terror experience. It is common for children between 6 and 12 years but can happen to anyone. Even though sleepwalkers are known to be completely harmless, they may injure themselves in the process.

Sleeping Cycles – Putting Them All Together

It is now clear that sleep is not uniform as it has distinctive stages that follow an easy-to-predict pattern. Standard sleep cycles begin with N1, go through N2 and N3, and finish with the REM sleep.

The N1, N2, and N3 stages are known as N-REM, or non-rapid eye movement sleep. The N1 phase creates a link between being awake and being in a deep sleep state. The N2 phase is when sleep spindles occur, which is essential for learning and memory.

During the deep, or N3, stage, growth, brain waste removal, cell renewal, and repair occur. It may seem like the stage of sleep that’s most important, but the others are equally vital. Whereas the sleeping cycle length changes throughout the night, the first phase remains shorter as compared to the rest.

Within an 8-hour sleep, you go through the five stages of sleep, and the cycle lasts about 90-110 minutes. Are you wondering, “What stage of sleep do dreams occur?” Dreaming happens during the REM stage. Throughout this period, pons, the brain part where REM signals originate, shuts off the spinal cord signals.
This action results in your body remaining still during the dreaming phase. It prevents people from acting what they are dreaming of. In turn, spinal cord signals shutting results in a considerable reduction in issues associated with working without sense inputs.

Are you feeling energized, rested, or curious at the moment? In your opinion, what sleep stage do you experience the most frequent? Is your sleep calm and regular? If you are among those who monitor their physiological state, a sleep cycle alarm clock can be a great option for improving your health and productivity. If you have any additional questions on sleep phases, leave your comment in the section below, and I will reply shortly.

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