What are the stages of sleep and how do they differ?

As humans, our sleep consists of two main stages, a) Rapid Eye Movement or REM sleep and b) non-REM sleep.

Non-REM sleep is divided into three stages:

  • Stage 1 is light sleep where someone can be easily awoken. Brainwave activity and muscle tone slows as does our heart rate and breathing. This stage lasts a few minutes.
  • Stage 2 still presents a light, restful sleep. However here, brainwaves further slow down with occasional bursts of activity. Core body temperature drops as the body prepares for deeper sleep. Together stages 1 and 2 comprise 35-40% of total sleep.
  • Stage 3 is the deep sleep phase characterised by extremely slow delta brainwaves. Blood pressure, breathing and heart rate reach their lowest levels. In this stage, growth hormone is released and promotes body repair and restoration. It’s very difficult to wake someone at this point. This stage represents around 15-25% of total sleep.

After deep sleep, REM or rapid eye movement sleep commences and this is where dreams occur. Brainwaves speed up and eyes move rapidly under closed eyelids. Skeletal muscles paralyse apart from maybe some intermittent twitching. Our breathing becomes irregular and our heart rate escalates. REM comprises 20-25% of total sleep.

These four sleep stages cycle in succession through night, allowing the body and mind to renew. The right quantity in each phase promotes optimal rest.

Disruptions to the different stages of sleep can adversely affect our mental and physiological functioning in the following ways:

  • Stage 1 – this transition to sleep phase allows the mind and body to start unwinding via slowed breathing, heart rate, muscle tone, and brain waves. Not getting enough would limit our ability to easily fall asleep.
  • Stage 2 – this further unwinding allows the body and mind to completely disengage from waking stimuli and resolve perspectives formed during the day. Lack of this stage of sleep can impact our ability to fully relax emotionally and mentally.
  • Stage 3 – the deep sleep initiates vital body tissue growth and repair by way of associated hormone releases. Muscles regenerate, tissue mends, blood sugar levels normalise, and essential immune system strengthening occurs. Skipping sufficient deep sleep robs the body of this restoration and may weaken natural immunity.
  • REM sleep allows the mind to organise information and learning through dream activity. It also regulates mood and emotional processing associated with memory integration and learning. Deprivation of REM sleep hinders memory, decision making, emotional stability and our ability to cope with stress or anxiety. Feelings of depression may also develop with extended REM loss.

Overall lack of sufficient time in each specific stage denies the body and mind the key physiological repair and important cognitive processing required for optimal daily performance mentally, physically, and emotionally.

To ensure you get the best from your sleep try to get between 7 and 9 hours a night. Take a look at our tips for good sleep to help you get the most from yours.