This article is from the Depression FAQ, by Cynthia Frazier with numerous contributions by others.
"Atypical depression" is not an official diagnostic category, but it is often discussed informally. A person suffering from atypical depression generally has increased appetite and sleeps more than usual. An atypical depressive may also be able to enjoy pleasurable circumstances despite being unable to seek out such circumstances. This contrasts with the "typical" depressive, who generally has reduced appetite and insomnia, and who is often unable to find pleasure in anything. Despite its name, atypical depression may in fact be more common than the other kind.