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Types of sleep

What happens when your head hits the pillow and you drift off to sleep? Your brain cycles between two different types of sleep —rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. Typically, people begin the sleep cycle with four stages of non-REM sleep, followed by a short period of REM sleep. Dreams generally occur in the REM stage of sleep.

What happens in non-REM sleep?

During non-REM sleep your brain is inactive but your body may still move around. There are four stages to non-REM sleep:

  • Drowsiness. Your muscles relax, your heart rate decreases and your body temperature lowers.
  • Light sleep. You’re unconscious and unaware of your surroundings, but even though you’re sleeping lightly you can still be roused. During light sleep, some people have sudden muscle contractions that are often preceded by a sensation of starting to fall or trip. These sudden movements are similar to the ‘jump’ we make when we’re startled.
  • Slow-wave sleep. Your blood pressure gradually falls. This is also when some people may talk or walk in their sleep.
  • Deep slow-wave sleep. It is difficult to be woken during this stage and you may feel confused if you are. As you get older, slow-wave sleep becomes less frequent and less deep. This means you wake up more easily.

During the deep stages of non-REM sleep, the body repairs and regenerates tissues, builds bone and muscle and appears to strengthen the immune system.

What happens in REM sleep?

REM sleep gets its name from the fact that the eye moves rapidly from side to side during this sleep phase. When you switch into REM sleep, your brain is active and your muscles become completely relaxed. During this time, your breathing also changes. It becomes more rapid, irregular and shallow, while your heart rate increases and your blood pressure rises. This is usually when you dream. When people wake up during REM sleep, they may be able to describe their dreams. The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep.

We lose some of our ability to regulate body temperature during REM sleep, so very hot or cold temperatures can disrupt this stage of sleep. According to the US National Institute of Neurological Disorders and Stroke, if our REM sleep is disrupted one night, our bodies won’t follow the normal sleep cycle progression the next time we doze off. Instead, we often slip directly into REM sleep and go through longer periods of REM until we ‘catch up’ on this stage of sleep.

How caffeine, alcohol and other drugs can all affect REM sleep

Because sleep is influenced by different nerve signals in the brain, some foods or medicines that affect these signals can also affect whether we feel alert or drowsy and how well we sleep. Caffeinated drinks such as coffee, tea and cola and some medications including decongestants can stimulate parts of your brain and make it difficult for you to sleep. 

Some antidepressants suppress REM sleep. Heavy smokers often sleep very lightly and have less REM sleep and they also tend to wake up after three or four hours of sleep due to nicotine withdrawal. Some people with insomnia may try to solve the problem with alcohol. But while alcohol can help people fall into light sleep, it also robs them of REM and the deeper, more restorative stages of sleep. 

Instead, it keeps them in the lighter stages of sleep from which they can be easily woken up.

Further information

Australasian Sleep Association


National Center on Sleep Disorders Research. Information on sleep. [online] Colorado Springs, CO: BSCS. c2003 [accessed 23 Aug 2010] Available from:

National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep. Bethseda, MD: National Institutes of Health. [last updated 21 May 2007, accessed 23 Aug 2010] Available from:

National Sleep Foundation. Sleep-wake cycle — its physiology and impact on health. [online] Washington DC: National Sleep Foundation. 2006 [accessed 19 Aug 2010] Available from: (PDF 2.6Mb)

Patlak M. Your guide to healthy sleep. Bethseda, MD: National Heart Lung Blood Institute. 2005.

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This information has been developed and reviewed for Bupa by health professionals. To the best of their knowledge it is current and based on reputable sources of medical research. It should be used as a guide only and should not be relied upon as a substitute for professional medical or other health professional advice.

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Last published 31 October 2010