What Is It?
In major depression, the most prominent symptom is a severe and persistent low mood, profound sadness, or a sense of despair. The mood can sometimes appear as irritability. Or the person suffering major depression may not be able to enjoy activities that are usually enjoyable.
Major depression is more than just a passing blue mood, a "bad day" or temporary sadness. The symptoms of major depression are defined as lasting at least two weeks but usually they go on much longer — months or even years.