Many people with depression also suffer muscle and joint pains, headaches, and fatigue.

Many people with depression also suffer muscle and joint pains, headaches, and fatigue.(PBNJ/BLEND/GETTY IMAGES)

Everybody feels down for a day or two. But one in 14 American adults—15 million in all—has clinical depression each year.

Depression is a complex condition characterized by profound sadness, lethargy, feelings of worthlessness, and a loss of interest in social activities. These feelings can last for two weeks or go on for decades. The difference between the blues and clinical depression is one of length and severity of symptoms.

"If you've gotten to the point where you're looking up depression on the computer, then there's a good chance it's a real depression, not the blues," says Tracey Lipsig Kite, MSW, a licensed therapist in private practice in Evanston, Ill. "If you really are to the point where you think you might need therapy, you're probably right."

Physical symptoms of depression
Depression doesn't always look or feel like a dark mood.

"Irritability is one of the most under-recognized symptoms of major depression," says Rakesh Jain, MD, director of psychopharmacology at R/D Clinical Research Center, in Lake Jackson, Tex.

Doctors also often overlook physical symptoms, says Dr. Jain. Some 67% to 69% of people who receive a diagnosis of major depression also have muscle and joint pain, headaches, and fatigue.

Sharon Charles Haznedar, an administrative director for behavioral health services at New York City's Saint Vincent Catholic Medical Centers and a psychiatric nurse practitioner, says depression is insidious because it often renders victims unable to ask for help: "I've had depressed patients tell me that they need a plan just to walk across the room."

"Depression drains a person's energy," Haznedar continues. "The idea of visiting the doctor, figuring out whether your insurance plan will cover the visit, and filling prescriptions can be daunting when you're depressed. If you're already seeing one or more doctors for other health conditions, the difficulties associated with another illness can be overwhelming."

Gender differences in depression
Women are twice as likely as men to be diagnosed with depression. However, men more often commit suicide as a result of this debilitating condition. And debilitating it is: Numbers from the National Institute of Mental Health indicate depression is the leading cause of disability in Americans between the ages of 15 and 44.

Depression begets more depression
Like an open wound or a broken bone, depression rarely heals itself.

Half of all people who have had one episode of depression and are not taking antidepressants will have another, according to The Harvard Medical School Family Health Guide. A second episode makes the risk of a third one even higher. A person who has had three episodes and is still not taking medication has a 90% risk of having a fourth.

And it's like falling downhill. Successive episodes tend to get more severe and occur more frequently. People with depression have an average of four to eight episodes in a lifetime.

"If you think you may be depressed, get an evaluation," says Walter Brown, MD, clinical professor of psychiatry at Brown University in Providence, R.I., and Tufts University School of Medicine in Boston. "If you had bad headaches or stomach problems, you'd see a doctor without hesitation. The same principle applies if you think you are depressed."