Answered by Irving I. Gottesman, Ph.D.:
The classification and understanding of the group of disorders where depression, or low mood, is a main feature is still unsolved. Optimal treatment depends on accurate classification. A thorough physical exam from your family physician is a good place to start to rule out an endocrine problem or other somatic causes. By using the search function at the NAMI Web page, you can look under depression, dysthymic disorder, and bipolar disorder to see the range of information available. Bereavement after a major loss in your life such as the death of a child or parent, a divorce, death of a pet, loss of your job, the impact of 9/11, all may resemble varieties of depressed mood but they usually get better with the passage of time. If not, seek professional help.