Sleep Stages and Sleep Cycles

Sleep cycles
Image: David Castillo Dominici /

The brain, it seems, needs to switch off from its conscious state for a certain period each day in order to ‘recharge’.
I say conscious state because, of course, it doesn’t shut down as such and can actually be very active.

Sleep Stages

You may have heard of 2 different patterns of sleep called REM sleep (characterized by Rapid Eye Movements which gives it its name) and Non-REM sleep and you may assume from the nomenclature that REM sleep is the most important and significant type of sleep. In fact, REM sleep is possibly the least important stage.

In fact, there are several stages of sleep, characterized partly by different types of brain wave and these stages recur cyclically. Knowing how the sleep stages work can be useful in planning sleep and even short naps.

Non-REM (NREM) sleep

There are 4 stages of non-REM sleep and the activity of the brain, measured by ‘brain waves’ changes for each stage.

Stage 1-2 ‘Light sleep’

The first two stages of sleep into which we fall can be categorized as Light. You can be woken easily without feeling any more ‘groggy’ than you did when you fell asleep. You can wake yourself, perhaps with a jerk, or even wake without even realizing you have been asleep. We only enter the 1st stage when we initially fall asleep, the 2nd stage constitutes the longest period of sleep under normal circumstances.

 Stages 3-4 ‘Deep Sleep’

The next two stages are when the brain really slows down and produces Delta waves, the slowest and largest amplitude waves and the furthest from your conscious state. It is much harder to be woken at this time and, if you are, you would feel groggy and disorientated. Ironically, perhaps, this is the stage at which sleep-walking or sleep-talking are most likely to occur and, after REM sleep, the time when you are most likely to dream.

This is also the type of sleep we miss most if it is lacking and which the body tries to catch up on, so the first session of Deep sleep is likely to be quite long.

One upshot of this is that if you are planning a nap, a short one may be of more use than a snooze of say an hour, as it is quite possible that you will be in Deep sleep when your alarm goes off and you may well wake up feeling worse.

 REM sleep

Not until the previous stages has occurred will you enter REM sleep. This is the stage most associated with dreams and, if woken, you are more likely to report a vivid dream. We still do not know why we dream but the fact that we do may indicate an importance that we don’t yet understand.

 Sleep Cycles

The whole sleep cycle described above, which may last between 90-100 minutes, is then more or less repeated, though there are some differences in the individual cycles.

Firstly, after the first time, stage 1 is omitted. (You can think of REM sleep as replacing stage 1).

Secondly, the duration of Deep sleep is gradually reduced while that of REM increases. If you have a normal, regular, trouble-free sleep pattern, you may only need two cycles of Deep sleep so, for the latter cycles, there will be no Deep sleep and you just cycle through stage 2 sleep and REM sleep until waking.

On the other hand, if you are severely lacking in sleep, you will have more Deep sleep and less REM sleep until your body feels it has recouped enough of it. So Deep sleep is what your body seems to consider the most important. This statement does of course disregard any sleep problems which may interfere with recovering sufficient sleep. These will be dealt with in separate posts.

 Why should we sleep early?

We are told that it is better to sleep and rise early – but why?

It is not to do with your sleep cycle as such, but due to the fact that your built -in detox organs, do their detoxifying mostly before or just after midnight.

For the lymph system it is before midnight and between around 11pm and 1am in the case of the liver. Because they work more efficiently when you are in the Deep sleep stages, not going to bed until 2am could, in theory, leave you more susceptible to certain illnesses.

Furthermore, remaining awake until late interferes with your natural production of melatonin which has an effect on the immune system.

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