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Definition

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

Alternative Names

Tiredness; Weariness; Exhaustion; Lethargy

Considerations

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 of 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. Because fatigue is a common complaint, sometimes a potentially serious cause may be overlooked.

The pattern of fatigue may help your doctor determine its underlying cause. For example, if you wake up in the morning rested but rapidly develop fatigue with activity, you may have an ongoing physical condition like an underactive thyroid. On the other hand, if you wake up with a low level of energy and have fatigue that lasts throughout the day, you may be depressed.

Common Causes

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 thyroid or overactive thyroid
• Use of alcohol or illegal drugs like cocaine, 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 lupus
• Cancer
• Chronic liver or kidney disease
• 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
• 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. Little relieves CFS, including rest.

Reviewer Info: Robert Hurd, MD, Professor of Endocrinology, Department of Biology, Xavier University, Cincinnati, OH, and physician in the Primary Care Clinic, Cincinnati Veterans Administration Medical Center, Cincinnati, Ohio. Review provided by VeriMed Healthcare Network., 07/17/2007