All depression types are not the same. Major depression, also known as clinical depression, and chronic depression, also known as dysthymia, are the most common types. But there are also other types of depression with unique signs, symptoms, and treatment.
According to the National Institute of Mental Health, major depressive disorder is characterized by a combination of symptoms that interfere with a person's ability to work, sleep, study, eat, and enjoy once-pleasurable activities.
There are times you may feel sad, lonely, or hopeless for a few days. But major depression -- clinical depression -- lasts longer and is disabling. It can prevent you from functioning normally. An episode of clinical depression may occur only once in a person's lifetime. More often, though, it recurs throughout a person's life.
In addition, with major depression, one of the symptoms must be either a persistent depressed mood or loss of interest. The symptoms should be present daily or for most of the day or nearly daily for at least two weeks. Also, the depressive symptoms must cause clinically significant distress or impairment in functioning. To "count" as a diagnosis of clinical depression, the symptoms cannot be due to the direct effects of a substance -- drug abuse, medications -- or a medical condition, such as hypothyroidism.
Persistent depressive disorder -- formerly known as chronic depression, or dysthymia, is characterized by a long-term (two years or more) depressed mood. There are also symptoms present that are associated with major depression but not enough for a diagnosis of major depression. Chronic depression is less severe than major depression and typically does not disable the person. If you have low-grade persistent depression, you may also experience one or more episodes of major depression during your lifetime.
Bipolar disorder -- sometimes referred to as manic depression -- is a complex mood disorder that alternates between periods of clinical depression and times of extreme elation or mania. There are two subtypes of bipolar disorder: bipolar I and bipolar II.
With bipolar I disorder, patients have a history of at least one manic episode with or without major depressive episodes.
With bipolar II disorder, patients have a history of at least one episode of major depression and at least one hypomanic (mildly elated) episode.