Knowing the Stages of Sleep Will Help You Know Yourself. Here's Why.

You have heard about the different stages of sleep. REM, deep sleep, light sleep... After reading this article, you'll know why sleep stages are important for your health and how you can find out whether you're getting enough of each sleep phase.

Published: April 2019, 16 minute read

There are 5 stages of sleep that follow each other in a cyclical fashion:

  

- wake 

- relaxed wakefulness

- light sleep

- deep sleep and

- REM sleep. 


Let's see what happens during each phase and how they affect you during the day. 

Since the advent of electric light, we’ve increasingly ignored and misunderstood sleep: It’s a necessary evil. It’s an inactive state. It’s the human stand-by mode. 


However, with advances in science and technology, and a budding revolution in attitudes towards sleep, we may be ready to throw these ideas into the dustbin of history.


These three states of being are found in nearly all mammals and birds: wakefulness, Non-REM sleep and REM sleep. From a physiological viewpoint they are as different from each other as sleeping is from being wide awake. You just don’t notice it – mainly because you’re asleep.

All mammals and birds sleep. Their sleep is divided into two states: REM (rapid eye movement) sleep and Non-REM sleep. This is the three-fold division of our existence: we’re awake, we’re sleeping and we’re dreaming.


REM sleep is a stage in which the brain is active but the body is paralyzed. The name comes from the fact that during REM sleep our eyes dart about underneath our eyelids. It’s during REM sleep that we have our most vivid dreams.


Non-REM sleep is a stage in which the brain is relatively inactive and our body is movable. Non-REM is further divided into stages based roughly on how deep the sleep is and how difficult it is to rouse someone from it.

Non-REM vs REM SLEEP

During rapid eye movement sleep we experience most of our dreams.

There are 5 stages of sleep. According to the American Association for Sleep Medicine (AASM) classification, there are 5 stages of sleep:


Stage W: Wakefulness

Stage N1: Relaxed Wakefulness

Stage N2: Light Sleep

Stage N3: Deep Sleep, or Slow-Wave Sleep (SWS)

Stage R: REM Sleep: Dreaming

The N in N1–N3 refers to Non-REM sleep. The AASM classification is the one used by Oura, except that we have combined N1 and N2 stages into one stage called Light Sleep.


Each sleep stage is characterized by changes in our physiology. However, the transitions between stages may not always be clear cut.

W, N1–N3 and REM: Stages of Sleep

Advanced sleep trackers like the Oura ring can show you how many minutes you spend in each sleep stage.

Stage N1 Sleep is a transition stage between wakefulness and the deeper stages of sleep. It is easy to wake up from this stage. During N1 you are aware of your surroundings but you become increasingly relaxed as you drift off to sleep. 


During the first sleep cycle, you usually spend less than 10 minutes in Stage N1 sleep. It accounts for approximately 5% of total sleep time.


PHYSIOLOGY OF N1 SLEEP


Core body temperature drops at sleep onset

Slow eye movements

Lack of sleep spindles in the EEG


EXPERIENCES DURING N1 SLEEP


Hypnic jerks

Illogical thoughts when drifting off to sleep

Reduced awareness of surroundings


FUNCTIONS OF N1 SLEEP


Transition from wakefulness to the deeper stages of sleep

N1 Sleep: The Transition Stage

The sudden jolt you sometimes experience when drifting off to sleep is called a hypnic jerk.

N2 Sleep: Light Sleep

Stage N2 sleep is stage of light, regenerating sleep. It is still relatively easy to wake up from this stage of sleep.


As you fall asleep, the muscles in your upper airway relax and make your airways narrower. Have you ever wondered how you know someone has fallen asleep watching the TV? Even if you don’t see whether their eyes are open or not? It is often the sound of their breathing that gives them away.


N2 stage sleep makes up the majority of our sleep: 45–50% in healthy young adults. With 8 hours of sleep, that is 3.5–4 hours of N2 stage sleep per night.


PHYSIOLOGY OF N2 SLEEP

Presence of EEG patterns: K complexes and sleep spindles

Decreased heart rate

Decreased blood pressure

No eye movements


EXPERIENCES DURING N2 SLEEP

Fragmented dreams

Brief arousals from sleep


FUNCTIONS OF N2 SLEEP

Rest and recuperation

N3 Sleep: The Brain Cleansing Deep Sleep

Stage N3 sleep, deep sleep or slow-wave sleep (SWS) is the most rejuvenating and restorative sleep stage. During deep sleep, the glymphatic system removes waste, such as neurotoxins and beta-amyloids, from the brain.


There are several ways to get more deep sleep, from establishing good sleep hygiene to taking hot showers before bed. However, keep in mind that all stages of sleep are important for health and good-quality sleep, not only deep sleep.


PHYSIOLOGY OF N3 SLEEP

EEG: slow-wave brainwaves

Decreased heart rate

Decreased blood pressure

Release of growth hormone

No eye movements


EXPERIENCES DURING N3 SLEEP

Very difficult to wake up from deep sleep

If awoken, disorientation and grogginess


FUNCTIONS OF N3 SLEEP

Cell repair and rejuvenation

Replenishing glycogen

Long-term memory

Removal of waste from the brain: glymphatic system

Deep sleep and meditation have been found to share similar brain cleansing benefits.

REM Sleep: The Dream Stage

REM sleep is a sleep stage in which the brain is active but the body is paralyzed. Vivid dreams happen during REM sleep and your heart rate and respiration rate are increased. In terms of brain activity, REM sleep resembles wakefulness.


You tend to get more REM sleep later in the night. REM sleep may be completely absent from the first sleep cycles of the night. 


REM sleep is linked to the circadian rhythm of our body temperature: our core body temperature starts to drop off when we fall asleep and reaches a nadir in the early morning hours. If you go to bed much later than usual, you may skip the first cycles of sleep (including regenerative deep sleep stages) and even go straight to REM sleep.


PHYSIOLOGY OF REM SLEEP

Rapid Eye Movements

Loss of muscle tone

Low amplitude mixed frequency EEG

Limited thermoregulation, shivering or sweating

Elevated heart rate

Elevated respiration rate


EXPERIENCES DURING REM SLEEP

Vivid dreams

Erections and blood flow to the genitals


FUNCTIONS OF REM SLEEP

Learning and problem solving

Memory consolidation

Mental health

Getting enough sleep consistently is vital for both physical and mental well-being.


Do you feel rested and energized during the day? If you do, you don’t have to worry about sleep stages. Your body is doing its job and stressing over percentages or minutes spent in each stage is counterproductive.


Do you feel tired during the day? Starting your journey towards better sleep and better health can start with tracking your sleep stages with something like the Oura ring.


And finally, do you feel rested, energized and curious? Consider getting a sleep tracker that tracks the stages of sleep. You might unlock the keys to better health and productivity by seeing what has previously been unseeable.

Sleep Stages. So What?

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