Understanding Sleep Cycles


You probably have a pre-bed sleep routine but what happens when your head actually hits the pillow? Understanding how sleep cycles work is important in order to maintain a healthy mind and body as lack of sleep can be really bad for your health. It’s not just feeling a bit grumpy or not being able to work at your best, lack of sleep can have profound effects beyond a simple bad mood or a lack of focus – it can affect your physical health.


Understanding how your sleep cycle works and what the stages of sleep are can help you sleep better.


A sleep cycle is the time it takes for you to progress through the five stages of sleep. You don’t go straight from closing your eyes to REM sleep, rather you cycle through stages from light sleep to deep sleep and REM sleep, before repeating that cycle again.


The stages of sleep are categorised into REM sleep (rapid eye movement) and NREM (non-rapid eye movement). Only in the final stage do you proceed to full REM sleep, while the other four stages are considered NREM sleep.


Typically, a sleep cycle lasts about 90 minutes and during that time you will move through the five stages of sleep. You will normally go through four or five cycles in a single night. During the first three cycles you will spend more time in NREM sleep, while in the final two cycles you will tend to spend more time in REM sleep.



At this stage you have just begun to fall asleep. This stage happens within minutes of you putting your head on the pillow. At this stage your brain produces waves that are called alpha and theta waves, and your eye movements begin to slow down. This stage of sleep is brief, lasting only about seven minutes. You are in a light stage of sleep which means you are still somewhat alert and can still be easily woken.



Here, you still sleep fairly lightly and your brain waves start to slow down, while producing very short periods of rapid, rhythmic brain activity often called Sleep Spindles. Your heart rate begins to slow down, your body temperature starts to drop, and your eye movement begins to stop. This stage lasts about 20 minutes.



Stages three and four are the deepest stages of sleep. At this stage, you find it hard to wake up and if you do, you will likely be disorientated and groggy for a few minutes after you awake.


These stages of sleep are most often grouped together as they are the periods of slow wave sleep. Here, your brain waves slow to what are known as delta waves, with the occasional faster wave interspersed into your sleep. As your body moves from stage three into stage four, the number of these delta waves increase, and the faster waves decrease.


In addition to this slower brain activity, your blood pressure drops further and your breathing becomes slower. At this stage, there is no eye movement and your body becomes immobile.


These stages of sleep are the ones that help rejuvenate your body. During the slow wave sleep, hormones are released that aid growth and appetite control. These help replenish muscles and heal damaged tissues that were used over the course of the day.


These are the stages where people, particularly children, are most likely to experience nightmares and sleepwalking.



Stage five of sleep is most often called REM sleep, and unlike every other stage of sleep, the brain is positively bursting with activity. The average adult spends roughly 20% of their sleep in REM, while infants and the elderly spend more time in REM.


REM sleep is called such because the eyes whiz in all directions while the limbs and muscles are temporarily paralysed. Breathing slows down as it becomes shallower and irregular, while your blood pressure and heart rate rise.


The vast majority of dreaming happens in this stage, which is as a result of the heightened brain activity which is almost the same as being awake. This stage of sleep helps to revitalises the brain, supporting your alert daytime function.



Now that you understand sleep cycles, you can figure out how to incorporate this knowledge into your sleep pattern. Your sleep pattern will change as you age, from as much as 16 – 18 hours of sleep as an infant, to as little as 6 hours for an elderly person. Even then, sleep patterns vary significantly across individuals of the same age so if you are getting more or less sleep, there is no need to worry.


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