Mood Disorders are mental illnesses in which the primary symptom is a mood disturbance. These conditions can include inappropriate, exaggerated or a limited range of feelings. We all have times of feeling down and at other times experiencing significant happiness. People who are diagnosed with a mood disorder, however, may experience these feelings on an extreme level or for excessively long periods. For example, they might feel very depressed and suicidal a lot of the time or, on the other hand, might experience excessive levels of energy, with little desire for sleep. The most common Mood Disorders are: Bipolar Disorder – in which a person experiences a pattern of mood cycles, combining depressive and manic episodes. Major Depression – when feelings of sadness, fatigue, and poor concentration interfere with everyday life over a long period of time. Dysthymia – a chronic, often milder depression that lasts for a long period of time (often years). Cyclothymia – in which the individual experiences milder mood swings, from euphoria to depression.