State of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli.

Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. Fatigue (in the medical sense) is sometimes associated with medical conditions including autoimmune disease, organ failure, chronic pain conditions, mood disorders, heart disease, infectious diseases, and post-infectious-disease states. However, fatigue is complex and in up to a third of primary care cases no medical or psychiatric diagnosis is found. Fatigue (in the general usage sense of normal tiredness) often follows prolonged physical or mental activity...