Fatigue is a frequent symptom in the general population, being reported by up to 50% of the respondents to large-scale surveys. It is attributable to underlying systemic diseases such as diabetes, cardiopulmonary disease, or rheumatoid arthritis, but may also accompany psychiatric conditions such as depression, panic disorder, or somatization. The etiology of isolated fatigue or fatigue associated with the symptoms of other minor illnesses is often undiagnosed and poorly treated. The word â€œfatigueâ€ can have various meanings, including exhaustion, a perceived decrease in the ability to undertake mental or physical activities, delayed recovery after demanding physical exertion, or weariness due to unrefreshing sleep. Self-reported fatigue is typically transient, self-limiting, and explained by prevailing circumstances, but a small minority of subjects experience persistent and debilitating fatigue. When fatigue cannot be explained by a medical condition such as depression, cancer, infections, or inflammatory disorders, it may be due to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a clinical diagnosis without any distinguishing physical or routine laboratory findings. Attempts have been made to establish whether its etiology is infectious, immunological, neuroendocrinological, psychiatric, or sleep-or malignancy-related, but no definite conclusion has yet been reached, and it seems likely that it is a heterogeneous illness that reflects a common pathway of various pathophysiological abnormalities that manifest themselves with similar symptoms.
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