When a person is asleep, the body goes through four different stages of sleep: breathing, recovery, muscle relaxation, and brain waves.
Stages of Sleep
In broad terms, sleep can be categorized into REM (rapid eye movement) and NREM (non-REM sleep). Most adults will start sleeping from a state of drowsiness into NREM sleep.
NREM sleep has three substages: stage N1, stage N2, and stage N2. While older classifications covered four NREM sleep stages, the current rules combine stage 3 and stage 4 into stage N3.
Sleep stage cycles typically last 90 to 120 minutes. Four to five cycles occur during a typical night of sleep.
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NREM Stage N1
This first NREM sleep stage is the typical transition from awake to asleep. It lasts for just a couple of minutes. It is the lightest sleep stage, and individuals who wake from it usually do not fall asleep.
In this stage, the eye movements are usually rolling and slow. One's heartbeat and breathing also tend to slow down as muscles start relaxing. A person also produces low-amplitude frequency waves within the theta range of 4 to 7 Hz.
NREM Stage N2
This next NREM sleep stage covers a significant percentage of the overall sleep time. It is thought to be a lighter sleep stage from which one can quickly wake up. This stage occurs before deep sleep.
During this stage, one's breathing and heartbeat become even slower. The eye does not move, and the body temperature goes down. K-complexes and sleep spindles also appear.
NREM Stage N3
This final NREM sleep stage is deep sleep, also known as delta or slow-wave sleep. During this stage, the body performs various crucial tasks for health promotion.
It isn't easy to arise from sleep in this stage. One's breathing and heartbeat also reach their slowest rate. The body gets fully relaxed, and no eye movements are present. There is also a marked presence of delta brain waves. This stage is also when tissue growth and repair, cell regeneration, and immune system strengthening happen.
REM Stage R
REM sleep comes in two phases, namely, phasic and tonic. The phasic REM sleep phase involves rapid eye movement bursts, while the tonic phase does not.
This stage, R, takes place roughly 90 minutes after falling asleep. It is mainly the dreaming stage of sleep. This stage typically lasts 10 minutes the first time, with its duration increasing in each REM sleep cycle. Its final cycle may last for around 30 minutes to one hour.
During this sleep stage, eye movements turn rapid during the phasic REM sleep phase. Heart rate and breathing increase and end up more variable. The muscles also get paralyzed, though there could be twitching at times. Brain activity also markedly goes up.
When a person sleeps through the night, they go through all these sleep stages several times. The entire cycle may last for roughly 90 minutes.
Improving Sleep Hygiene
Good sleep hygiene is critical to attaining quality sleep. Some ways to boost sleep hygiene include spending time under the sun, moving the body, or exercising during the day, limiting nap time to just 20 to 30 minutes, avoiding stimulants before bedtime, limiting screen time before sleeping, and creating a comfortable environment for sleeping.
Following such tips over time could significantly enhance sleep quality. However, if problems with falling or staying asleep persist, a checkup is recommended.
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