What Are the Stages of Sleep?

Getting 8 hours of sleep matters. So does getting the right kind of sleep. Some forms of sleep are better for your body and brain than others.

Keep reading to learn about things like non-REM, REM, and slow-wave sleep – what they are, why they’re different, and how they support your health. (Skip to the end for 5 practical tips on improving your sleep quality.)

The Stages of Sleep

Sleep isn’t monolithic. Like your waking hours – when your circadian rhythm controls your energy levels – slumber has different stages. You oscillate between 4 different types of sleep every 90 minutes:

• Non-REM stage 1
• Non-REM stage 2
• Non-REM stage 3
• REM

But those stages aren’t evenly distributed over each 90-minute cycle. Earlier in the night, your cycles will be dominated by non-REM stage 3 sleep. In the second half, though, most of your time will be spent in REM sleep.

There’s a reason for such complex sleep architecture. Each of the different stages has a unique role in maintaining your physical and mental health. Here’s a brief overview of how they work.

Wakefulness

You’re awake for around two-thirds of your life. Most of that time is spent upright and alert, but you might also experience wakefulness during the night – brief blips of consciousness that interrupt your sleep.

Brainwaves during wakeful periods are either:

• gamma waves (30 to 100 hertz), which occur during periods of high stress and deep concentration
• beta waves (13 to 30 hertz), which are your ‘default’ waking waves
• alpha waves, (8 to 13 hertz), which occur during periods of relaxation.

NREM Stage 1 Sleep

Non-rapid-eye-movement (non-REM or NREM) sleep is divided into 3 stages. You enter the first stage, N1, when you fall asleep. Your body isn’t fully relaxed, but your brain starts displaying theta waves – longer, slower oscillations of 4 to 8 hertz [2]. Your breathing remains even and regular.

NREM Stage 2 Sleep

The second stage of non-REM sleep, N2, is still classed as light sleep. Unlike N1, though, it also features delta waves (0.5 to 4 hertz) – long, low rhythms that sweep across your brain from the front to the back.

NREM Stage 3 Sleep

After N2, you sink into the third stage of non-REM sleep. This is deep, heavy sleep dominated by delta waves, which is why it’s often known as ‘slow-wave sleep’ or ‘SWS’. N3 is the sleep stage responsible for repairing your muscles and supporting your immune system.    

REM Sleep

During the final stage of a sleep cycle, you transition into rapid-eye-movement (REM) sleep. This is the stage your dreaming intensifies. Your muscles become totally slack, and your brainwaves accelerate from delta to beta – the same high-frequency, chaotic rhythms you produce when you’re awake. Your breathing also becomes shallower and more erratic. 

What Is Light Sleep (N1 and N2)?

N1 and N2 – collectively referred to as ‘light sleep’ – make up around 50% of your total sleep volume [2]. (N2 comprises around 45%, while N1 takes up just 5%.)

N1 is a transitional sleep stage. It’s how your body makes the shift from wakefulness to slumber, which is why it only occurs after you’ve been awake.

N2, on the other hand, is true sleep. Your brain starts producing delta waves, and both your heat rate and body temperature drop further. It’s also characterised by 2 very interesting types of brain activity: sleep spindles and K-complexes.

If you watched a recording of your brain activity during N2 sleep, you’d notice brief flurries of activity, each one lasting for around a second. Those flurries, which range from 10 to 15 hertz, are called sleep spindles, and they’re essential for memory consolidation [3].

If you kept watching, you’d occasionally see something else: a sharp, steep spike, then a deep trough, followed by an even larger, longer spike [4]. That’s a K-complex. Scientists still aren’t sure why they occur. Like sleep spindles, they might help consolidate your memories – or serve an entirely different purpose, like supporting the connections between different parts of your brain [4].

What Is Deep/Slow-Wave Sleep (N3)?

The third stage of non-REM sleep, N3, is also known as deep or slow-wave sleep (SWS). During slow-wave sleep, your brain displays long, slow delta waves. That’s not because it’s dormant or inactive [1]. It’s because your brain cells are all working together to do things like [5]:

• consolidate your memories
• even out connections between each other (which makes your brain more efficient)
• replenish the energy they’ve spent during the day
• reduce levels of cortisol (the stress hormone), epinephrine and norepinephrine (both part of your body’s fight-or-flight response)
• increase growth hormone, prolactin, and melatonin (the sleep hormone)
• support your immune system’s health
• clean out toxic waste products that may cause conditions like dementia.

The release of growth hormone is one reason why slow-wave sleep is so important for our bodies’ growth and recovery.

What Is REM Sleep?

You’ve probably heard of rapid-eye-movement (REM) sleep. It’s when our bodies become totally limp – but our brains go into overdrive.

We start producing beta waves (the same type of brainwaves we make when we’re awake). Our breathing becomes shallower and more erratic [6]. Our heart rate and body temperature both go up [6]. Our eyes move around rapidly under closed lids. Occasionally, one of your legs or arms might jerk – a movement known as a ‘myoclonic twitch’ [7].

Scientists still aren’t sure what purpose REM sleep serves. We know it plays a key role in memory consolidation (although how that happens isn’t clear) [6]. It’s also when we dream – another sleep phenomenon we know very little about.

Some other benefits of REM sleep may include:

• emotional processing [8]
• greater creativity [9]
• better problem-solving abilities [10].

How to Measure Your Sleep Stages

When we sleep, we’re unconscious. That might seem obvious, but it’s why all of us are very bad at measuring how much sleep we get [11]. We often recognise when we haven’t sleep enough – we feel tired, we know we went to bed too late – but we struggle to actually put a number on things like total sleep time.

So, if you want to measure how much slow-wave and REM sleep you’re getting each night, you need a tracking device. Currently, those come in 2 varieties:

• heart rate trackers, like Whoop, Oura, and Apple Watch
• brainwave trackers, like Muse.

For most people, a watch-like heart rate tracker is the easiest and most affordable option. Most modern wearables use a blend of signals (heart rate, heart rate variability, respiratory rate, and movement) to accurately gauge different sleep stages. You can normally view your sleep data using an app on your phone.  

How to Improve Your Sleep Stages

Many factors can affect your sleep quality. Those include age, sleep disorders, medication, and mental health. In most cases, though, simple lifestyle changes can make a big difference.

Here are 5 tips you can try tomorrow night.

1. Follow your chronotype’s wind-down routine.
   1. Don’t know your chronotype? Take the test here – 60 seconds, no email required.
2. Create a sleep sanctuary. That means investing in a high-quality sleep surface in a cool, dark, distraction-free space.
   1. If you have an adjustable sleep surface, try sleeping in the zero-gravity position.
3. Ask your doctor about taking electrolytes before bed. A good-quality blend can help you relax, stop muscle cramps, and make you less likely to go to the toilet at night.
4. Add background noise to your sleep sanctuary. Try brown noise, gentle nature sounds (like surf, running water, or wind), or even just your fan.
5. Align your daily routine with your chronotype. Light exposure, exercise, good eating patterns, and less stress can all help you sleep better.

The information contained in this article is general information only. It should not be construed or used as medical or healthcare advice. For personalised advice, book a consultation with a qualified and registered medical or allied healthcare professional.