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Stages of Sleep

Sleep is a sort of “system shutdown” all humans perform on a regular basis, to be able to keep functioning.

From a scientific perspective, sleep is much more complicated than simply catching some shuteye.

Stages of Sleep

In this piece we’ll take a look at what the 5 stages of sleep are, what sleep patterns are and how long a sleep cycle is – among other things.

What are the five stages of sleep?

Until not so long ago, it was believed that sleep was nothing more than a period of time spent in passive rest, while unconscious.

Nowadays we do know though that there’s quite a bit going on during sleep.

Various sleep stages alternate and rotate, each one putting in its own contribution towards the rejuvenation and regeneration of the body and mind.

Stage 1

The first stage of sleep is one most people are actually aware of, when they’re in it.

Just as you are drifting off to sleep, you might hear an ambient sound getting further and further away from you.

During this stage, you are essentially slipping in and out of consciousness. Muscles sometimes jerk during this stage of NREM sleep, awakening you momentarily.

When you truly fall asleep, Stage 1 transitions into Stage 2, which is still in the NREM realm.

Stage 2

During Stage 2, your heart rate decreases and your body temperature drops. Despite that, Stage 2 is still considered relatively light sleep.

A person spends around 50% of the time spent sleeping in this stage.

Stage 2 sees alternating muscle contractions and relaxation, the pausing of eye movement and the slowing down of brain waves.

Deep Sleep

Stage 3 and Stage 4 are the two deepest stages of sleep. Waking up from one of these stages is the most difficult, and if you do actually wake up during these stages, you will feel disoriented and physically drained.

These two stages are both SWS (Slow Wave Sleep) stages, meaning that they are characterized by the slowing of brain waves. These slow waves are known as Delta waves.

During this stage, the blood pressure drops further and muscle movement stops. Despite that, the body retains its ability to move muscles if needed.

This stage is the one where nightmares strike, and childhood bed-wetting happens during this stage as well.

Sleepwalking and other sleep disorders rear their heads at this point too.

Fraught with so many potential problems, these two sleep stages are perhaps the most useful in terms of rest and rejuvenation. It is during these sleep stages that various hormones are replenished, exerting control over growth as well as bodily functions such as appetite.

Those into fitness and bodybuilding probably know that this is the stage they need most to replenish their aching muscles, since this is where the increasing blood flow transports vital nutrients and oxygen to repair and to build tissue.

REM Sleep

Stage 5 is where REM (Rapid Eye Movement) comes into the picture. During this stage, the mind begins to “power up,” getting ready for awakening.

Adults typically spend some 20% of their sleep in this stage. Toddlers on the other hand, can spend as much as 50% of their sleep in the REM stage.

Dreams (and nightmares) occur during this REM stage.

A good night’s sleep consists of 4-6 such cycles (stages 1 through 5). Not being able to cycle through these stages enough times will result in sleep deprivation, exhaustion and impeded bodily functions.

What are the stages of sleep in psychology?

Psychology defines the 5 stages of sleep described above, although in some cases, you will indeed find them described somewhat differently. Some of these definitions set REM sleep completely aside from the other 4 stages for some reason.

The 4 stages you’re then left with are often defined based on the reduction in Alpha brain waves. Thus, stage one sees a reduction of about 50% in these waves, compared to awake resting with one’s eyes closed.

Stage 2 is the realm of “spindles” and K-complexes, while Stage 3 ushers in Delta waves, which take over and grow stronger, being present 20%-50% of the time.

Stage 4 is where these Delta waves exceed the 50% mark. This is – as said above – the deepest stage of sleep, and the most benefic part in regards to regeneration and hormonal replenishment.

Long story short: despite some differences in the definitions, the 5 stages covered are the same as the ones I described in detail above.

What is a normal sleep pattern?

In order to get the most out of your sleep (and believe me, you need to do just that), you have to make sure your sleep pattern is as close to normal as possible.

What is a normal sleep pattern though?

Ideally, and from a scientific perspective, normal sleep pattern sees the alternation of the above described stages of sleep in the above described manner.

Sleep patterns do shift over one’s lifetime though, and they are affected by seemingly “minute” factors too, such as the amount of recent sleep one had, various sleep disorders, one’s sleep schedule and of course: age.

In newborns, for instance, the sleep cycle might start off in the REM stage. The various NREM/REM stages that follow are much shorter than in adulthood (instead of ~90 minutes, these stages last only ~50 minutes). “Proper” sleep patterns and fully developed stages usually emerge after 2-6 months. As the brain evolves with age, so do sleep patterns.

Sleep history is certainly a major factor though, over which you actually retain control. Missing out on proper sleep several nights in a row, will lead to a redistribution of your sleep stages, resulting in longer slow-wave NREM sleep, needed to catch up on regeneration and replenishment.

Chemicals, such as alcohol, also have a major impact upon the sleep stages, as do daytime naps. While such naps will turn a typical 8-hour single-block sleep pattern upside down, they aren’t necessarily unhealthy or counterproductive from the perspective of “proper” sleep. As long as their length is kept under 60 minutes, these naps won’t result in the person falling into deep sleep.

One thing that’s certain about daytime naps though is that they will aggravate insomnia, so if you are an insomnia sufferer, you should probably steer clear of daytime napping.

What is the deepest stage of sleep?

As mentioned above, your sleep is the deepest during stages 3 and 4. It has to be noted that sometimes, these two stages are lumped in together, being treated as a single stage. What makes these sleep stages so deep though?

Starting about 35-45 minutes after you fall asleep, this deep-sleep stage is characterized by the slowing of the brain waves. Alpha waves give way to Delta waves, which are slower and larger, breathing becomes more uniform and deeper as well and waking up drifts off into the distance.

Indeed, it is most difficult to wake up during this stage, and people who are awakened while in deep sleep will feel disoriented, and will often experience literal physical discomfort. Headaches may strike out of the blue if woken up from stage 4 deep sleep too.

Needless to say, while in this stage of sleep, the senses of the sleeper become dulled. This explains why a person in this stage of sleep is most likely to sleep through outside disturbances without exhibiting any kind of reaction.

Which is the most important stage of sleep?

As I already made it clear above, every sleep stage has its role in the regeneration and replenishment of the organism, but the stage that the body seems the keenest to catch up on when proper sleep patterns are disturbed, is REM sleep.

A “normal” sleep patterns starts off with NREM sleep – as mentioned above – but when a person fails to get enough sleep, he/she may actually slip right into REM sleep instead, as a way of compensating.

REM periods may be extended too, to catch up on lost “quality” sleep.

Called the restorative part of the sleep cycle, REM sleep is aimed at the regeneration and “re-setting” of the mind. No wonder that this is the stage where most dreams occur.

While no one fully understands the importance and role of dreams yet, I suspect that they may be the brain’s way of processing information, dealing with emotions and settling memories.

With that in mind it is obvious that although not yet fully understood, the importance of REM sleep for brain regeneration cannot be underestimated.

How long is a full cycle of sleep?

A full cycle of sleep encompasses all 5 above-discussed sleep stages, and overall, it lasts for about 90 minutes (an hour and a half).

During a proper night’s sleep, you will go over several such sleep cycles (in 8 hours, that would amount to ~5 such full cycles.

The length of each cycle may vary from person to person, and it depends on a number of variables, such as the amount/quality of sleep the person got beforehand, the age of the person, his/her psychological state, etc.

Do dreams last for 3 seconds?

No. Dreams can vary in length from a few seconds to 20-30 minutes. They mostly occur during the REM stage of sleep – as said above – and they are best remembered if the dreamer is awakened during the REM stage.

An average on the number of dreams you may have during one night is 3-5. Some people may have as many as 7 dreams.

Most of these dreams are forgotten immediately though, so people will have no recollection of the vast majority of dreams they have.