Depression- a depressed mood and/or extreme sadness that becomes debilitating causing a sever disruption of daily life; there are several forms: major depression, bipolar disorder, seasonal affective disorder, and dysthmia
*symptoms: misery, despair, guilt, feelings of worthlessness, no hope for the future, thoughts of suicide, withdraw from human contact, no interest in life, can't feel pleasure, may become fretful, irritable, and unable to concentrate, etc.