The clinical term depression most often refers to major depression, also known as major depressive disorder. This mood disorder causes persistent sadness and a loss of interest in normal activities or things a person used to enjoy.
If you have depression, you likely have many other symptoms, but these two are the most characteristic signs of major depression. Other symptoms include difficulty thinking, feelings of guilt or shame, irritability, and changes in sleep or eating patterns.
Major depression causes symptoms severe enough to interfere with your daily activities. They typically persist daily for at least two weeks.
Persistent Depressive Disorder
Persistent depressive disorder (PDD) is also known as dysthymia. It is a chronic, long-term type of depression that lasts for at least two years. The symptoms are similar to those caused by major depression but are generally not as severe.
Even though PDD symptoms are milder, they can fluctuate from mild to moderate and sometimes be severe. The symptoms never go away for longer than a couple of months at a time. They can also impair normal functioning and interfere with normal activities.
To other people, someone with PDD may seem fine, if a little gloomy. Although you may be better able to cope with daily life with this condition as compared to major depression, it still causes significant distress and dysfunction.