What Causes Extreme Fatigue?

Everyone experiences occasional bouts of tiredness, often due to overwork or lack of sleep. However, people with extreme fatigue typically experience a profound lack of energy and tire easily despite adequate rest and sleep. Many diseases and conditions affecting different body systems can cause this symptom. Diagnosis of the underlying cause of extreme fatigue facilitates the development of a treatment plan to help diminish this frequently debilitating symptom.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.


Infections -- especially viral infections -- are among the leading causes of extreme fatigue. Common, short-term viral illnesses associated with extreme fatigue include influenza and infectious mononucleosis. Other possibilities include viral hepatitis, Lyme disease and HIV/AIDS. Although relatively uncommon in the U.S., active tuberculosis is also often characterized by extreme fatigue.

Anxiety and Depression

Major depression and anxiety disorders affect millions of Americans, and extreme fatigue is a frequent symptom of these conditions. Difficulty falling asleep and/or staying asleep may be a contributing factor to the fatigue experienced with these disorders. However, even people who experience relief of other symptoms of depression while on medication sometimes report persistent fatigue.


Anemia -- a condition characterized by an abnormally low number of red blood cells circulating in the bloodstream -- is a common cause of fatigue. The degree of fatigue increases in proportion to the severity of the anemia. Additionally, long-standing anemia can adversely affect heart function, further aggravating fatigue. Iron deficiency is the most common cause of anemia. However, many genetic and acquired diseases can also cause anemia, such as sickle cell disease, peptic ulcer disease and Crohn disease.

Heart Diseases

Heart failure describes the condition in which diminished heart function leads to insufficient oxygen-rich blood delivery to body tissues, resulting in chronic fatigue. The level of fatigue increases as heart function decreases. Among people with advanced heart failure, fatigue typically proves severe. Different types of heart disease can lead to heart failure, including coronary artery disease, hypertensive heart disease and cardiomyopathy. Infective endocarditis -- an infection of the interior of the heart -- can also cause extreme fatigue.

Lung Diseases

Lung diseases that significantly diminish the capacity to extract life-sustaining oxygen from the air frequently cause extreme and persistent fatigue. Examples include cystic fibrosis, chronic obstructive pulmonary disease and pulmonary embolism -- blood clots lodged in the lungs. Short-term fatigue is common with pneumonia.

Hormonal Diseases

Hormonal diseases encompass a variety of illnesses that can affect the rate of energy generation and usage in the body. Several of these disorders can lead to profound fatigue, such as an underactive thyroid gland or pituitary gland, diabetes, abnormal function of the adrenal glands, and acromegaly -- a condition caused by excessive production of growth hormone.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

A February 2015 report issued by the Institute of Medicine estimates that 836,000 to 2.5 million Americans suffer from myalgic encephalomyelitis, also known as chronic fatigue syndrome. This disorder is characterized by activity-limiting fatigue of at least 6 months duration that isn't attributable to another medical cause. A variety of other symptoms may accompany the condition, including headaches, body aches, poor concentration and forgetfulness.

Other Causes

Several other diseases may cause extreme fatigue, including autoimmune disorders such as lupus and giant cell arteritis. Neurological disorders such as multiple sclerosis and Parkinson disease can also cause this symptom. Chronic kidney or liver failure are also possibilities. Medication side effects, nutritional deficiencies and poisoning are other considerations.