Fatigue is a feeling of weariness or exhaustion of strength. It is under the control of the nervous system, although the exhaustion of body tissues is a frequent contributing factor. People who are stimulated or inspired by certain kinds of work readily continue to work even with aching muscles. Also, people may become fatigued without having exercised, because of disturbances affecting the nervous system, such as fear, anger, or boredom. In normal conditions fatigue can be a pleasant experience, especially if it is remedied properly by such measures as eating and sleeping. Excessive fatigue, mental or physical, always requires rest.