Sleep Health

What happens during sleep?

Before you start to hack your sleep, it is important to get a solid understanding of how sleep works. Humans need sleep. Some animals are lucky and don’t need much sleep (Giraffe’s sleep for only 5 minutes at a time, for a max of 2 hours per day!), however humans typically need 6-10 hours of sleep to be fully functional.

There are a few states where your body performs certain metabolic processes. Sleep, Excercise, Digestion.

During sleep, your body focuses its’ energy on repairing the body. If you don’t get enough quality sleep, your body doesn’t get the chance to repair itself properly, and you will end up with an increased risk to a whole raft of diseases.

Within sleep itself, there are several different states of  sleep, which are very important to understand. Two major categories are Rapid Eye Movement (REM) and Non-Rapid Eye Movement (Non-REM).  Throughout the night, we go through several cycles of sleep. The first cycle takes approximately 60-90 minutes to complete, after this NREM and REM sleep alternates for the rest of the night.

Two main types of sleep, courtesy of Dr C Dement.

Stages of Non-REM Sleep

Stage 1

This is the transition period from wakefulness to the other stages of sleep. During Stage 1 NREM there is typically an extremely low threshold of arousal very easy to wake someone who is in this stage of sleep). Stage 1 sleep typically lasts only a few minutes, and marks the transition from Awake State to the Sleep State.

Stage 2

This stage of sleep makes up around 45% of the typical persons night sleep.

Stage 3 – Deep Sleep

Typically lasts a few minutes, and is a transition between Stage 2 and Stage 4 NREM sleep.

Stage 4 – Deep Sleep

Extremely high threshold of arousal (difficult to wake someone who is in this stage of sleep).  Generally, the first sleep cycle has the largest amount of Stage 4 deep sleep, which lasts for 20-40 minutes. The duration of Stage 4 sleep decreases for every subsequent sleep cycle as the night progresses.


REM – Rapid Eye Movement

Extremely high threshold of arousal (difficult to wake someone who is in this stage of sleep). Dreams often occur during REM sleep, however they do tend to be less vivid compared to NREM dreaming. During REM sleep, the brain is incredibly active. This is understandable in order for the brain to create an environment, populate a scene, and act out the dream – it is not uncommon for muscles to actually twitch during this stage. The first REM period of the night typically lasts for only 1-10 minutes. The duration of REM sleep increases for every subsequent sleep cycle as the night progresses. After REM stage, there is a brief period of awakening, before proceeding to another NREM cycle.


Courtesy of Dr William C. Dement

Stages of Sleep Courtesy of Dr William C. Dement

Images and content from this page borrowed from Dr William C. Dement’s website. See my recommended resources page where I recommend his book for those who want to learn some serious detail about sleep.



  • First Sleep Cycle typically lasts 90-120 minutes, this is the predominant time for deep sleep to occur (20-40 minutes). REM sleep lasts only 1-10 minutes.
  • Second Sleep Cycle typically lasts 100-110 minutes, less deep sleep occurs during this phase. REM sleep duration increases to 10-20 minutes.
  • Third Sleep Cycle onward typically involves little or no deep sleep. NREM is made up of mostly Stage 2 sleep. REM duration increases up to 30-45 minutes in the later cycles (Lots of dreaming).
  • After REM cycle, a brief awakening period occurs, before re-entering NREM cycle. This is the perfect time to wake up!


Sleep and Restoration

Deep sleep is typically attributed to be the restorative, though this has not yet been scientifically proven. My personal experience tracking my sleep using Sleep as Android, I need to have more than 50% ‘deep sleep’ to feel restored in the morning. I typically wake up with energy after 7.5 hours sleep – so long as I’ve had good quality sleep. See my blog for more examples of some interesting experiences I’ve had using Sleep as Android.


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