depression

A group of emotional reactions frequently characterized by sadness, discouragement, despair, pessimism about the future, reduced activity and productivity, sleep disturbance or excessive fatigue, and feelings of inadequacy, self-effacement, and hopelessness. In some individuals, such traits may be mild, intermittent, and undetectable by observers, but in others they may be constant and intense. In its more- severe forms, pathology may be a manifestation of a major affective disorder, bipolar disorder, or cyclothymic disorder. See also exogenous depression and endogenous depression.