Fatigue has two meanings.
It may be felt as a general sense of weakness, lack of energy, tiredness, and sometimes extreme sleepiness. Or it may simply be weakness and pain in a set of muscles , especially the limbs or back, after heavy use. In some illnesses, however, fatigue may persist day after day despite efforts at sleep and renewal. In such cases the fatigue may be caused by a serious underlying condition that can often respond to treatment. Causes Easily corrected fatigue results when the body's stored energy is used up and its waste products build up in body tissues.