Major depression is a serious clinical mood disorder in which a person experiences extended periods of sadness, emptiness, frustration, anger, and despair. The symptoms are so severe that they can interfere with the person's ability to work, sleep, study, eat, and enjoy activities that they once found pleasurable. Some people with major depression may feel that life is not worth living and some will attempt to end their lives.An episode can occur only once in a person’s lifetime, but more often than not, a person has several episodes. They may also take place spontaneously, during or after the death of a loved one, a breakup, a medical illness, or other major life event.