Depression

Depression is remarkably common. More than 5 percent of Americans—some 18 million people—suffer from clinical depression at any given moment. Another 5 percent experience mild symptoms or feel blue. At least one person in six has a serious depressive episode during his or her lifetime. For some people, depression is caused by an imbalance of chemicals, or hormones, in the body. A person's mood sometimes depends on the chemical makeup of those hormones. If they are out of balance, the person can become depressed.

Experts say that 70 percent of people treated for depression will experience the illness again. Usually, those later periods of depression are less severe than the first. One out of every three people who have suffered from depression never has another serious problem with it.