What is the Sleep Cycle?

guy sleeping on couch

Sleep is a very interesting phenomenon that is more important than we think. It can make or break us in more ways than one, so it is definitely important that we know and understand what happens when the lights go out for the night. Everyone knows sleep is important for their health and wellness, but regardless, many people fail to get enough sleep. According to a National Sleep Foundation (NSF) survey, over 40 million Americans suffer from 70 different sleep disorders, and 60 percent of adults report having sleep troubles a few nights a week and more!

Sleep Architecture? Is That a Thing?

Many of the ill effects that accompany sleep deprivation or specific disorders are made mysterious due to a lack of understanding of one’s sleep architecture. Yes, “sleep architecture” is a thing. Just as building architecture looks at the ways of organising materials and structures to construct an edifice, sleep architecture describes the cyclical organisation, depth and duration of stages of sleep. To get a picture of this, specialists normally utilise what is called a hypnogram (a graph which shows information captured from an EEG over a course of sleep).

simplified sleep phases

From a sleep architecture perspective, whenever we go to bed each night we are engaging with two major categories of sleep: REM and NREM. REM (Rapid Eye Movement) describes sleep characterised by electrical activity in the brain which closely resembles wakefulness (along with notable eye movement). This is also the stage in which sleep paralysis will tend to occur because the body effectively turns off most muscular activity. NREM (Non-REM) on the other hand is characterised by slower brain waves and limited muscular activity. How much time we spend in each is a function of several variables, but shifts will occur as we age or incur a sleep deficit for any period of time. Normally you’ll pass through each around 4-5 times each night, with NREM sleep dominating for the earlier portion, and REM sleep slowly taking the lion’s share towards morning. The progression is normally denoted as NREM1, NREM2, NREM3, and then in reverse with REM occurring last before the start of a new cycle. Missing stages may indicate sleep disorders (eg. narcolepsy patients progress straight to REM without passing through NREM).

Sleep fulfills both mental and physiological needs. Each category of sleep is intended to help the body recover and prepare for the wear and tear of the next day. Even minimal sleep loss may affect your energy, mood, efficiency, and ability to manage stress. If you want to stay healthy, or you want to be in your best form, you shouldn’t consider sleep as a luxury. Let’s examine what happens in each category and shed some light on the process.

NREM Sleep

Let’s talk about NREM sleep first. This category officially has 3 stages associated with it (NREM1, NREM2, NREM3), with the last being a merger of the original stages 3 and 4. Overall you’ll spend around 75%-80% of your entire sleep time in this zone. In real terms, this amounts to around 4-6 cycles per night, each one being around 90 minutes in length.

Stage 1 (NREM1)

This is the lightest stage of sleep usually when you are just drifting off. As you go in and out of sleep, the eyes move slowly, breathing becomes regular and muscle activity decreases.Your brain waves move from the more rapid beta profile to the slower, more synchronised alpha profile.
Ever been jerked awake suddenly due to a strange sensation of falling? This is the stage in which sudden twitches or ‘hypnic jerks’ are likely to happen. Interestingly enough, persons with irregular sleep patterns tend to have more of these!

drowsing and nodding off

Watching persons nod off can sometimes be rather entertaining…

In this stage of sleep (also known as drowsy sleep), you can be awoken quickly. In fact, persons awoken from this state oftentimes believe they have never slept at all (I once had a friend on the graveyard shift who always proclaimed this time and time again without fail). Insofar as time is concerned, it is quite short, lasting usually less than 10 minutes, which equates to somewhere around 5% of one’s total sleep time.

Stage 2 (NREM2)

sleep-spindle-and-k-complexIn stage 2 the eye movements stop, and your breathing slows right down. Your body temperature decreases and your heart rate and blood pressure decrease as well. Your brain waves also slow down and more closely match the theta profile. They are however occasionally interspersed with bursts of rapid brain activity called sleep spindles and K-complex brain wave patterns. It is believed that these help to reduce the responsiveness of the brain to external stimuli that it does not deem threatening, thus helping the sleeper to rest more deeply. This stage is also beneficial for information processing and the consolidation of memories. Its existence is perhaps one of the compelling reasons for the old adage ‘sleep on it’ which explains why many of us can do pretty well with memory recall of complex information after a good night’s sleep!

This stage usually lasts only 25 minutes, but is the longest phase by proportion (between 45%-50% of total sleep time). It’s where you’ll spend most of your time during the night mostly because it progressively lengthens per cycle.

Stage 3 (NREM3)
tired and groggy toon

This is how you would look if someone woke you during NREM3

In this stage, sleepers are completely unresponsive to external stimuli. Blood pressure, heart rate and body temperature are also at their lowest throughout this period. This is also known as deep sleep, and it’s very difficult to arouse sleepers in this phase. If you’ve ever felt like a train wreck after someone gave you a rude awakening, you’ve probably been bounced out of this stage. Disorientation and grogginess typically come into play for a few minutes after coming directly out of this phase, and it can take as long as 30 minutes for persons to fully become alert.

Extremely slow brain waves known as “Delta waves” present themselves alongside alongside occasional rapid brain activity (sleep spindles). Stage 4 was used to indicate a point further along in the continuum of deep sleep where delta waves occur more than 50% of the time.

Growth and tissue restoration are known to occur within this phase. For kids it’s especially important that this stage of sleep be taken seriously, since overall bodily development is dependent in part on this period.

This stage tends to be longest during the first half of the night and goes anywhere between 20 and 40 minutes in the initial cycle. Proportionally, it makes up around 15-20% of the total sleep time.

REM Sleep

simplified sleep phases

At one point sleep paralysis was considered to be demonic oppression! (Painting by Henry Fuseli – 1781)

Overall, REM takes up approximately 20%-25% of the entire sleep cycle. This is a fascinating stage of your sleep cycle because it’s where the most activity happens. Your breathing suddenly becomes quicker although shallow. Brain activity increases to a state similar to that of being awake. Your blood pressure rises slightly and your heart rate increases. For this reason, REM is also known as ‘paradoxical sleep’ since it so closely resembles wakefulness.

REM starts approximately 90 minutes after you first begin to sleep, with a duration of around 5 minutes in the initial cycle. As our sleep cycle progresses REM periods lengthen and deep sleep time decreases. It is at this stage that we tend to have vivid and memorable dreams. We also do some level of memory consolidation during this period, though not to the same extent as in NREM. A very interesting feature here is sleep paralysis, which prevents us from ‘acting out’ our dreams or nightmares. I, for one, am very grateful for that. I sometimes have dreams about zombies and I certainly wouldn’t want to be acting out my survival scenario during the night. My spouse would definitely not be amused!

How Sleep Cycles Change With Age

baby and dad sleepingNewborns have a fairly different kind of sleep architecture as compared to older kids, teens and adults. Since they don’t have a proper sleep-wake cycle, and oftentimes sleep up to 18 hours per day, their sleep episodes are a bit different. At the age of 3 months however, their sleep cycles regulate to more closely resemble the general architecture that holds true for for children up to adults.

Young children and adolescents tend to require less sleep in the day unlike infants. The former display a greater tendency towards REM sleep than the latter. The latter on the other hand may undergo different changes based on sleep hygiene, but time spent in NREM2 tends to increase with REM either remaining constant or decreasing.

tired old manAs we get along in age as adults, our sleep architecture will undergo very natural shifts. We will tend to get less deep sleep (NREM3) and stay longer in light sleep (NREM1). This really makes it tough on the elderly as they may have a hard time falling asleep and staying asleep at night. Obviously this can lead to a host of other health issues because we tend to get less restorative sleep as we age. It’s no surprise then that the elderly oftentimes need to sleep in the day in order to ‘keep up’.

Protecting Your Sleep Cycle

To avoid any disruptions in your sleep cycles or problems concerning the inability to reach even the sleep stage one, it is quite important to establish a regular sleeping routine or pattern (see 5 Tips for Great Sleep for more information). Learn to break the habit of taking caffeinated drinks or alcohol and smoking very near your bedtime. Since sleep would only occur once you are relaxed and composed, make it a point to de-stress long before bedtime through different ways, like meditating, performing breathing exercises, and other calming activities that will help in naturally inducing sleep. Exercising a few hours before bed can also ensure that your sleep progresses with minimal disruption.

little girl sleeping

The most important factor to remember is that it is the deep sleep stages that are most beneficial to us as this is where the body re-energizes and recuperates. So if we spend most of our time in light sleep (which is easily disrupted), then no matter how much sleep we have, we will wake up feeling tired and fatigued! So the bottom line is that it is not merely the quantity of sleep that you have, but also the type of sleep that you get throughout the night.

I do hope you found this informative. If you have any comments or queries, why not drop me a line in the comments area below? I look forward to hearing from you.

Sleep well until next time!



  1. jschicanha

    my parents use to be blaming me for sleeping a lit and sometimes regard me as the lazy person because i slept too much but after just reading the article about the sleeping cycle i have now found out that i was not wrong in some ways

    thanks for sharing this information

    1. Joshua (Post author)

      Thanks Jose, I’m glad you found this to be informative. If you were sleeping a lot and not feeling refreshed that could probably have pointed to something else that needed resolution. I do hope you’re getting the right amount of sleep now! If you ever have any further queries or concerns, don’t hesitate to give me a shout.

  2. Jacob

    Very informative post! No wonder sometimes no matter how long I sleep, I just feel so tired. I guess I am not into the “deep sleep stages”.

    Just some experiences that I thought I could share: Never get yourself too excited when you are about to sleep. I once played intense computer games and went straight to bed. I was practically awake for the whole night. Like what you said, we need to be relaxed enough before sleeping.

    What are your thoughts on sleep walking? When one is sleep walking, are they in the deepest level of their sleep?

    1. Joshua (Post author)

      Thanks for sharing Jacob. It’s definitely important to focus on preparing the body for sleep so that you can get optimal quality. In terms of sleepwalking, you are correct! Persons experiencing sleepwalking usually have these episodes during deep sleep (NREM stage 3). It tends to occur on the way back up to REM (going from NREM3 to NREM2) in the natural sleep cycle. You can check out my post on What Causes Sleepwalking in Adults for more details.

  3. Simon Crowe in Asia

    Many times I’ll have an issue I’m trying to decide the best way to deal with or a decision I’m trying to make and I’ll purposely put it at the forefront of my mind as I’m going to sleep. The next morning, may times think just seema lot simpler, easier and I have a solution.

    I also keep a notebook next to my bed for the same reason, I wake up with my best creative ideas just as I wake up.

    So this is my habit, but it’s fascinating to read some of the science behind it. I need at the very least 7 and a half hours of sleep otherwise I get grumpy. Eve if it’s just 7 hours I notice a difference.

    Thanks Josh for a really interesting article, I learned a lot today about sleep : )

    1. Joshua (Post author)

      Awesome Simon! Glad you see the importance of getting proper sleep–it can really up your game 🙂

      All the best!


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