Fatigue (also called exhaustion, lethargy, languidness, languor, lassitude, and listlessness)'s a state of weariness. It can describe a range of afflictions, varying from a general state of to a specific work-induced burning sensation within one's muscles. It can be both physical and mental. Physical fatigue's the inability to continue functioning at the level of one's normal abilities. It's in everyday life, but usually becomes particularly noticeable during heavy exercise. Mental fatigue, on… (More on Exhaustion)