Barbara Bowman thought the lethargy she has felt since early childhood was due to laziness. As a teacher, wife and mother in Virginia, she would often become argumentative, and then have attacks of remorse. Marriage counseling led her to individual therapy that finally diagnosed dysthymia—mild, chronic depression that can sometimes last for decades.

Persistent feelings of hopelessness, irritability, low self-esteem and low energy are among the signs of dysthymia (dis-THY-mia). Officially, it's when someone has a dark mood...