A normal nights sleep has three main parts.

• Quiet sleep. This is divided into stages 1-4. Each stage becomes more 'deep'. Quiet sleep is sometimes called deep sleep.
• REM (Rapid Eye Movement) sleep. REM sleep is when the brain is very active, but the body is limp apart from the eyes which move rapidly. Most dreaming occurs during REM sleep.
• Short periods of waking for 1-2 minutes.

Each night, about 4-5 periods of quiet sleep alternate with 4-5 periods of REM sleep. In addition, several short periods of waking for 1-2 minutes occur about every two hours or so, but occur more frequently towards the end of the nights sleep. The graph below shows a typical normal pattern of sleep in a young adult.
Normally, you do not remember the times that you wake if they last less than two minutes. If you are distracted during the wakeful times (for example, a partner snoring, traffic noise, fear of being awake, etc), then the wakeful times tend to last longer, and you are more likely to remember them.

What is insomnia?

Insomnia means poor sleep. About 1 in 5 adults do not get as much sleep as they would like. Poor sleep can mean:

• not being able to get off to sleep.
• waking up too early.
• waking for long periods in the night.
• not feeling refreshed after a nights sleep.

If you have poor sleep, you may be tired in the daytime, have reduced concentration, become irritable, or just not function well.

What is a normal amount of sleep?

Different people need different amounts of sleep. Some people function well and are not tired during the day with just 3-4 hours sleep a night. Most people need more than this. To need 6-8 hours per night is average. Most people establish a pattern that is normal for them in their early adult life. However, as you become older it is normal to sleep less. Many people in their 70s sleep less than six hours per night.

So, everyone is different. What is important is that the amount of sleep that you get is sufficient for you, and that you usually feel refreshed and not sleepy during the daytime. Therefore, the strict medical definition of insomnia is "a persistent difficulty falling or staying asleep, leading to impairment of daytime functioning".

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