• Definition

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

    Alternative Names

    Tiredness; Weariness; Exhaustion; Lethargy


    Fatigue is different from drowsiness. In general, drowsiness is feeling the need to sleep. Fatigue is a lack of energy and motivation. Drowsiness and apathy (a feeling of 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 sign of a more serious mental or physical condition. 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 it is usually not due to a serious disease.

    The pattern of fatigue may help your doctor determine its cause. For example, if you wake up in the morning rested but quickly develop fatigue with activity, you may have a condition such as 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 causes of fatigue, including:

    • Anemia (including iron deficiency anemia)
    • Depression or grief
    • Medications such as sedatives or antidepressants
    • Persistent pain
    • Sleep disorders such as insomnia, obstructive sleep apnea, or narcolepsy
    • Thyroid gland that isunderactive or overactive
    • Use of alcohol or drugs such as cocaine or narcotics, especially with regular use

    Fatigue can also occur with 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
    • Fibromyalgia
    • 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. It is diagnosed after all other possible causes of fatigue are ruled out. Most people with CFS do not get much relief from rest.