All to often I fall short with my sleep, waking up tired and flat.  I’m not alone – many kiwi’s (*1) feel they don’t get enough sleep most nights. However last night I’m stoked to say was not one of those nights! According to the SLEEP CYCLE app (iOS) I was in bed for close to 8 hours and spending most of in deep restorative sleep! (see above image)

Sleep is a foundational part of our wellbeing in respect to mind, body and ‘soul’ (*2) – which is why I’ve been monitoring it. In order to improve the quality of my sleep I need to understand it first. I’ve spent the last few weeks researching the science of SLEEP in particular Sleep Cycles and Circadian Rhythm. I tried to keep this as simple as possible – only because I am.

Sleep Cycles

Sooooo… we sleep in cycles – which fluctuates between Non-Rapid Eye Movement Sleep (NREM) and Rapid Eye Movement Sleep (REM) – a cycle is made up of 4 stages and can last, on average between 90 and 110 minutes.

The first 3 stages of sleep are considered NREM abbreviated as N1, N2 and N3.

N1 – The lightest stage of sleep – between wakefulness and sleep

N2 – A Slightly deeper stage of sleep

N3 – Deep sleep

REM – Rapid Eye Movement happens beneath your lids and is the fourth stage of sleep. Most of our dreaming occurs at this stage. Our voluntary muscles (*3) are paralysed – which is probably a good thing, otherwise we might physically re-enact our dreams in bed! Our brains are active – almost mimicking our daytime activity.

In a normal night of uninterrupted sleep we cycle through these stages 4 or 5 times, as mentioned each cycle averaging between 90 and 110 minutes.

The order of the stages isn’t sequential we usually go from:
N1 > N2 > N3 > N2 > REM – then we start back at N1 – to begin the next cycle. The duration of each stage depends on, how old we are and partially how long we’ve been asleep. We tend to do more Deep Sleep (N3) in the initial few hours of sleep and more REM sleep before we wake up.

What is our bodies response to each of these stages – and the benefits?

N1 –  During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches. 

N2 – Your heartbeat and breathing slows, and muscles relax even further.  Your body temperature drops and eye movements stop.  Brain wave activity slows but is marked by Sleep Spindles – brief bursts of electrical activity. At this stage we begin to process our memories and emotions.

N3 – Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and your brain waves become even slower.  Body repairs muscles, tissue and bones through secretion of important hormones and increased blood supply. Strengthening of the immune system.

REM – There is mixed frequency brain wave activity.  Our breathing becomes faster and irregular, and our heart rate and blood pressure increase to near waking levels.  Most of your dreaming occurs during REM sleep, although some can also occur at N3. REM increases the learning & memory function. This is when your brain consolidates & processes information from the day before, so that it can be stored in your long-term memory.

Additionally research suggests that sleep helps detox the brain – kind of like a plumbing system that flushes away toxins and resets from the previous day’s activities (*5). Scientist suggests a connection with  Dementia and Alzheimers from a build up of these toxins .  It’s not clear to me at what sleep stage the detox happens.

Circadian rhythm (also known as: internal biological clock or body clock)

A circadian rhythm is a regular 24 hour rhythm that controls many of our bodily functions including feeding, sleeping, body temperature and hormone production. The process of sleeping and waking up is controlled by the hormones Melatonin and Serotonin, which is heavily affected by darkness and light. 

Melatonin is activated when it get darker at night – it makes us feel tired
and gets the body ready for sleep.

Serotonin is activated when we are exposed to light, which wakes us up and gives us’ pep in our step’ to get amongst the day!

NOTE: artificial lights such as screens messes with our circadian rhythm and hence messes with our sleep.

ADDITIONALLY – Sleep-wake homeostasis keeps track of your need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger every hour you’re awake and causes you to sleep longer and more deeply after a period of sleep deprivation. (*5)

Apologies for how long this post is…ordinarily I’d prefer to keep things short bite sized and snappy. My reasoning is I’ve tried to group relevant information together so it presents logically AND makes sense to me and is hopefully of value to you!


(*1) A quarter of New Zealanders have a chronic sleep problem, according to the World Association of Sleep Medicine.

(*2) Whatever this means to you!

(*3) defined as muscles under or control or will – most skeletal movement is voluntary – for example legs and arms

(*4) NIH-funded study suggests sleep clears brain of damaging molecules associated with neurodegeneration.

(*5) https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep