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People with chronic fatigue syndrome feel extremely tired and weak most of the time. They often have other signs of illness, too.

There is no simple test for the condition, so your doctor will look for a collection of symptoms before deciding whether you have it.

Your doctor might decide you have CFS if:¹

• You have been feeling exhausted for at least six months for no obvious medical reason and not because of physical activity
• The tiredness makes you much less active than usual and is not made better by resting
• You also have four or more of these signs of illness: trouble remembering things, muscle pain, joint pain, headaches, sleep that doesn't make you feel refreshed, feeling much worse after exercise or activity, and tenderness in your groin or armpits, or behind your ear.

If you are worried that you or your child might have chronic fatigue syndrome, you should see your doctor. The doctor will probably first carry out some tests to rule out other causes of your tiredness.

Other conditions that can make you feel extremely tired include:^{1 2}

• A physical illness, such as an infection you've had for a long time, anemia, problems with your thyroid gland, or diabetes
• Mental health problems, including some types of depression
• Dementia
• Eating disorders like anorexia and bulimia
• Alcohol or drug abuse
• Ongoing stress in your personal life, or at work
• Being seriously overweight (obese).

If you're a woman, your tiredness could also be caused by pregnancy or by changes in your hormones if you're close to menopause.

It is important for your doctor to be sure that no other problems are causing your symptoms. If you do have another condition, your doctor might be able to cure it with the right treatment.

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.