Highs may alternate with lows, or the person may feel both extremes at close to the same time.
Professionals also refer to manic-depressive illness as bipolar mood disorder.
Manic-depressive illness usually starts in adult life, before the age of 35. Although rare in young children, it does occur in teenagers. This illness can affect anyone. However, if one or both parents have manic-depressive illness, the chances are greater that their children will develop the disorder. Manic-depressive illness may begin either with manic or depressive symptoms.