A major depression symptom can result from a single traumatic event in your life, or may develop slowly as a consequence of numerous personal disappointments and life problems. Some people appear to develop the symptoms of a major depression without any obvious life crisis causing it.
Major depression can occur once, as a result of a significant psychological trauma, respond to treatment, and never occur again within your lifetime. Some people tend to have recurring depression, with episodes followed by periods of several years without it, followed by another episode, usually in response to another trauma. In general, the treatment is similar, except that treatment usually is over a longer time period for recurrent depression.
Professional debate continues regarding whether some people develop "endogenous depression" without any identified psychological causes. This is a biologically caused depression, due presumably to either genetic causes or a malfunction in the brain chemistry. After psychological treatment and recovery from depression, the brain chemistry returns to normal, even without medication
Medication treats the symptoms of depression, and is often a vital part of the treatment program, but it is essential to treat the psychological problems that caused the depression.
Remember, only physicians are qualified to prescribe medication. Unfortunately, many poorly trained counselors never move beyond providing supportive counseling. This alone will not eliminate the depression. Supportive counseling "feels" helpful, and as part of the overall treatment plan does help. But, unless the depressed person makes critical life changes, the depression will continue. These changes are both internal and external.