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Insomnia is poor-quality sleep. You may find it difficult to get to sleep or to stay asleep at night. You may wake early in the morning or not feel refreshed when you get up.

Some people only have problems sleeping for a short time, whereas others have longer-lasting insomnia.¹

• Temporary insomnia can happen for a couple of days to people who usually sleep well. Your sleep may be disturbed by noise, shift work, jet lag or short-term anxiety or depression.
• Short-term insomnia may last for a few weeks. And it may happen again. You may find it difficult to sleep because you're worried about something (such as an illness or anxieties about money) or because of an emotional problem (such as coping with the death of someone close to you).

If you've had problems sleeping on at least three nights a week for one month or more, you probably have longer-lasting (or chronic) insomnia.²

Some people don't sleep well because of a medical or psychiatric condition, such as sleep apnea, depression or dementia. If you have one of these conditions, you may sleep better if it's treated. (To learn more about these conditions, see our information on sleep apnea, depression and dementia.)

Here we're looking only at chronic insomnia that hasn't been caused by any other illness. This is known as primary insomnia.

We don't know for sure why some people have problems sleeping and others don't. But we do know that:^{2 3 4}

• You're more likely to have problems sleeping if you're over 65. This may be because of changes in your body clock (your circadian rhythm) that can happen as you get older
• Changes in your life as you get older can make the changes to your sleep pattern seem worse. You may become less satisfied with sleep
• You might be more likely to have sleep problems if you are stressed
• Some people have trouble sleeping because they are too alert, aware or wakeful
• Napping during the day might make it harder to sleep at night. But in some countries people regularly take an afternoon "siesta" without any problems
• Stimulants can interfere with your sleep. These include alcohol, nicotine from smoking, and caffeine from tea, coffee, chocolate and sodas
• Some medications can disturb your sleep. These include diuretics (water pills), steroids, beta-blockers and some painkillers
• Some people may just need less sleep. How long people sleep and what they think is normal varies a lot. Most people sleep for between six hours and eight hours a night. But you may find you sleep less as you get older.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.