Major Depression
Major depression is more than just a passing blue mood, a "bad day" or temporary sadness over a specific event. The mood changes that come with major depression last for at least two weeks, and usually much longer.

Chronic Sadness (Dysthymia)
Have you been sad your whole life? Do you experience major periods of depression, over and over again? You may be experiencing a disorder called dysthymia, which is characterized by chronic sadness.

Bipolar Disorder
Have you found that your mood fluctuates from one extreme to another? Such mood changes may be a symptom of bipolar disorder, a form of depression.

Cyclothymia, a Less-Severe Type of Bipolar Disorder
The highs and lows of cyclothymia are less extreme than the highs and lows of bipolar disorder, although they are more troublesome than the usual ups and downs of life.

Seasonal Affective Disorder
Some people find that their moods shift with the seasons. The winter doldrums are not rare, especially in areas of the country where the winters are cold and long.

Postpartum Depression
Postpartum refers to the period immediately after childbirth. Symptoms of depression that occur during this period are known as postpartum depression. Other symptoms of mood disorder such as sleeplessness, irritability and anxiety, also can occur.