Fatigue, as a symptom, refers to a sense of lethargy or loss of energy. Fatigue is common in infections, endocrine disorders, heart failure, chronic diseases of the lungs, liver or kidneys, malignancies, anemia, nutritional deficits, inflammatory arthritis, Parkinson’s disease, depression, anxiety states, effect of certain medications, or drug withdrawal [1]. Population-based studies show that fatigue is one of the most common somatic symptoms, with as much as 20± 30% of the population complaining of chronic fatigue [2]. Only a small fraction of these satisfy the clinical definition criteria for chronic fatigue syndrome [1].
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Source: Naschitz JE, Sabo E, Dreyfuss D, Yeshurun D, Rosner I. The head-up tilt test in the diagnosis and management of chronic fatigue syndrome. Isr Med Assoc J. 2003 Nov;5(11):807-11. https://www.ima.org.il/FilesUpload/IMAJ/0/54/27402.pdf (Full article)