Maybe you get the blues from time to time or you feel grief over the loss of a loved one. These feelings are an unavoidable but normal and temporary reaction to life's stresses. There's a point, though, when the intensity and length of those feelings let us know that the depression has stopped being a temporary mood and has become a serious disorder.
Depressive disorders come in various forms.
Some people who suffer from a major depressive disorder have symptoms so severe they are unable to function at all. Other people have ongoing, chronic, milder symptoms. Some experience serious, recurring emotional lows and highs. This emotional roller coaster is called bipolar disorder or manic-depressive illness. Depressive disorders are the most common of the mental illnesses, but are also the most responsive to treatment.