Knowing how much time you spend in light, deep, and rapid eye movement (REM) sleep can help you understand a lot about your mood and levels of tiredness during the day.

Sleep researchers divide sleep into five stages—stages 1, 2, 3, and REM.

The five stages of sleep are:

• WakeThe first stage of sleep, which can be characterized by open or closed eyes 
• N1The first stage of non-rapid eye movement (NREM) sleep, which is characterized by light sleep and theta waves on an EEG 
• N2The second stage of NREM sleep, which is characterized by deeper sleep, regulated breathing and heart rate, and a drop in body temperature 
• N3The third stage of NREM sleep, also known as slow-wave sleep (SWS), which is characterized by deep sleep, relaxed muscles, and low breathing and heart rates 
• REMThe stage of sleep when rapid eye movement occurs, brain waves are similar to those when awake, and the body becomes temporarily paralyzed while dreaming 

A typical night’s sleep consists of four or five sleep cycles, each lasting about 90 to 120 minutes. As the night progresses, people spend more time in REM sleep and less time in deep NREM sleep

Deep sleep is essential for health and wellbeing. Most adults need around 1.5–2 hours of deep sleep per night. 

REM and deep sleep complement each other, with REM sleep supporting cognitive and emotional health and deep sleep focusing on physical restoration.

Sleep can be measured in waves on an electroencephalogram (EEG)

• Beta wavesThese waves are present when you are awake and alert, and have a frequency range of 13–15 to 60 Hz. 
• Alpha wavesThese waves are present when you are awake but have your eyes closed, and have a frequency range of 8–12 Hz. 
• Theta wavesThese waves are associated with emotions, memory, and activity in the limbic system, and have a frequency range of 3–8 Hz. 
• Delta wavesThese waves are present when you are in deep sleep or in a coma, and have a frequency range of 0.5–3 or 4 Hz. Delta waves are the slowest brain waves. 

To monitor your sleep cycles at home

Most smart watches now have sleep monitoring apps on them.

Typically they will measure 4 stages of sleep.

Tips for better sleep