Fatigue is a feeling of weariness, tiredness, or lack of energy.

Tiredness; Weariness; Exhaustion; Lethargy

Fatigue is different from drowsiness. In general, drowsiness is feeling the need to sleep, while fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of indifference or not caring about what happens) can be symptoms that go along with fatigue.

Fatigue can be a normal and important response to physical exertion, emotional stress, boredom, or lack of sleep. However, it can also be a nonspecific sign of a more serious psychological or physical disorder. When fatigue is not relieved by enough sleep, good nutrition, or a low-stress environment, it should be evaluated by your doctor. Fatigue is a common symptom, and is usually not due to a serious disease.

There are many possible physical and psychological causes of fatigue. Some of the more common are:

• An allergy that leads to hay fever or asthma
• Anemia (including iron deficiency anemia)
• Depression or grief
• Persistent pain
• Sleep disorders such as ongoing insomnia, obstructive sleep apnea, or narcolepsy
• Underactive or overactive thyroid gland
• Use of alcohol or drugs such as cocaine or narcotics, especially with regular use

Fatigue can also accompany the following illnesses:

• Addison's disease
• Anorexia or other eating disorders
• Arthritis, including juvenile rheumatoid arthritis
• Autoimmune diseases such as systemic lupus erythematosus
• Cancer
• Congestive heart failure
• Diabetes
• Infection, especially one that takes a long time to recover from or treat such as bacterial endocarditis (infection of the heart muscle or valves), parasitic infections, AIDS, tuberculosis, and mononucleosis
• Kidney disease
• Liver disease
• Malnutrition

Certain medications may also cause drowsiness or fatigue, including antihistamines for allergies, blood pressure medicines, sleeping pills, steroids, and diuretics.

Chronic fatigue syndrome (CFS) is a condition that starts with flu-like symptoms and lasts for 6 months or more. All other possible causes of fatigue are eliminated before this diagnosis is made. Most people with CFS do not get much relief from rest.

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