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Fatigue, Tiredness, and Lethargy: Symptoms & Signs

  • Medical Author: Melissa Conrad Stöppler, MD

Tiredness is not a symptom that defines any one particular disease. Rather, tiredness can be a symptom of many different diseases and conditions. Causes of tiredness range from lack of sleep and over exercise to medical and surgical treatments. The lack of energy (lethargy) associated with tiredness can sometimes cause difficulty with normal daily activities, leading to problems with attentiveness and concentration.

Fatigue, in medical terminology, refers to the state of reduced capacity for work or accomplishment following a period of mental or physical activity. For example, muscles fatigue if the are called upon to repetitively work for an extended period. Most of the causes of tiredness are also associated with fatigue.

A related term is lethargy. Lethargy refers to a state of lacking energy. People who are experiencing fatigue or tiredness can also be said to be lethargic because of low energy. The same medical conditions that can lead to tiredness or fatigue can also lead to lethargy.

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REFERENCE:

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

Medically Reviewed by a Doctor on 6/27/2019

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