Postpartum depression, however, is dark, intense, and long-lasting. The important thing is to seek help and don't blame yourself.
Postpartum depression is thought to be caused by low levels of the hormone cortisol.
Cortisol is normally released during times of stress. It raises blood sugar levels and regulates your blood pressure. Cortisol levels rise right before childbirth, then fall dramatically afterward. However, not every woman becomes depressed after childbirth, so this theory is still being questioned. You'll find a link to a book on overcoming postpartum depression on my Books page.