Depression affects a person's moods, thoughts, body, and behavior. There are three main types of depression, though within each the number of symptoms, their severity, and their persistence vary by individual. Major depression includes a combination of symptoms that interfere with a person's functioning. Episodes can occur once or several times within a lifetime. SAD appears to arise from a person's sensitivity to the limited amount of daylight that corresponds with seasonal changes.
Symptoms typically begin in the fall, worsen in the winter, and improve in the spring.
Dysthymia involves chronic symptoms that don't disable but prevent a person from feeling good. However, a person with dysthymia can have episodes of major depression as well. There is no single cause. Some depressive episodes appear for no reason. Diminished financial resources and social isolation also can be triggering circumstances.