Teen's pervasive sadness may be sign of serious depression

Dear Doctor K: My daughter is a high school senior. She's become extremely sad and uncharacteristically moody. Is she just a "normal" teenager, or could this be more serious? Dear Reader: Many teenagers have emotional ups and downs. But in some cases, a teen's sadness goes beyond normal "blues" and turns into depression. It's more likely to be clinical depression when the sadness is severe; lasts for more than a few days; or makes it hard to function at home, school, work or play. It's...