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What is fatigue?

Fatigue is a feeling or sensation of tiredness, weariness, exhaustion, weakness or low energy that occurs during or after routine activities. Fatigue can also be a feeling of inadequate energy to begin such activities. Fatigue is a symptom of a wide variety of mild to serious diseases, disorders and conditions including infection, inflammation, trauma, malignancy, chronic diseases, autoimmune diseases, and mental illnesses.

Fatigue can occur in any age group or population, but it is particularly common in the elderly and in people with chronic diseases. Depending on the cause, the sensation of fatigue can last briefly and disappear quickly, such as after exertion or a single night of insomnia. Fatigue can also be chronic and ongoing over a longer period of time, such as with fatigue due to chronic fatigue syndrome, depression, or heart failure.

Fatigue can be a symptom of a serious or life-threatening condition. If you experience fatigue that is not alleviated with good sleep habits and adequate nutrition, seek prompt medical care and talk to your medical professional about your symptoms. If you, or someone you know, is experiencing fatigue with chest pain, difficulty breathing, dizziness, or a change in consciousness or alertness, seek immediate medical care (call 911).

What other symptoms might occur with fatigue?

Fatigue may occur with other symptoms that vary depending on the underlying disease, disorder or condition. For example, fatigue caused by hypothyroidism may be associated with dry, brittle hair, hair loss, unusual weight gain, and possibly goiter (neck swelling due to enlargement of the thyroid gland). Fatigue associated with depression may occur with excessive crying, insomnia and apathy.

Symptoms that may occur with fatigue include:

Serious symptoms that might indicate a life-threatening condition

In some cases, fatigue can indicate a serious or life-threatening condition, such as acute heart failure or gastrointestinal bleeding, which should be immediately evaluated in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms:

What causes fatigue?

Fatigue can be caused by a wide variety of diseases, disorders or conditions, such as anemia, low blood pressure (hypotension), chronic fatigue syndrome, and Addison's disease. Although fatigue can be due to relatively mild and temporary conditions, such as jet lag, fatigue can also be caused by serious or life-threatening conditions, such as organ failure or cancer.

Fatigue that lasts for more than six months, is not alleviated by rest, and is not due to a known mental or physical illness is defined as chronic fatigue syndrome (CFS). The cause of CFS is not known at this time.

Common causes of fatigue

Fatigue can be due to common conditions including:

Other causes of fatigue

Fatigue can be due to a variety of other diseases, disorders and conditions including:

Medications that can cause fatigue

Always tell your doctor about any medications or supplements you are taking, including prescription and over-the-counter medications and herbal or alternative supplements. The following medications may be a possible cause of fatigue:

  • Antidepressants

  • Antihistamines

  • High blood pressure medications or diuretics

  • Sleeping medications, tranquilizers, sedatives, and anti-anxiety medications

  • Steroids

Questions for diagnosing the cause of fatigue

To diagnose the underlying cause of fatigue, your doctor or licensed health care practitioner will ask you several questions related to your symptoms. You can best help your health care practitioner in diagnosing the underlying cause of fatigue by providing complete answers to these questions:

  • Describe the fatigue. Is it constant or intermittent? Is it mild, moderate or severe? Does it occur with or after certain activities or events, such as stress, exercise, or just before the menstrual period?

  • How long have you had fatigue?

  • What other symptoms do you have with fatigue?

What are the potential complications of fatigue?

Complications associated with fatigue can be progressive. It is important to visit your health care provider promptly when you experience unexplained fatigue. Once the underlying cause is diagnosed, following the treatment plan you and your health care provider design specifically for you can help reduce potential complications including:

  • Decreased overall quality of life

  • Depression

  • Inability to perform daily tasks and disability

  • Malnutrition from loss of appetite associated with fatigue

  • Poor quality of life

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Dec 10
  1. Fatigue. Medline Plus, a service of the National Library of Medicine National Institutes of Health.  http://www.nlm.nih.gov/medlineplus/ency/article/003088.htm
  2. Chronic fatigue syndrome (CFS). Centers for Disease Control and Prevention. http://www.cdc.gov/cfs/general/index.html
  3. Tierney LM Jr., Saint S, Whooley MA (Eds.) Current Essentials of Medicine (4th ed.). New York: McGraw-Hill, 2011.
  4. Ricci JA, Chee E, Lorandeau AL, Berger J. Fatigue in the U.S. workforce: prevalence and implications for lost productive work time. J Occup Environ Med 2007; 49:1.
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