The term "depression" is often used to describe a very normal emotion that passes quickly. Everyone feels "down," "blue," or sad occasionally. But major depression is a "whole-body" illness, affecting the way a person eats, sleeps and feels about one's self. It is not a passing blue mood. People with major depression often feel sad, helpless, hopeless, and irritable.

Although it is perfectly normal to experience these feelings occasionally, people suffering from clinical depression cannot simply "snap out of it." It is the persistence and severity of these emotions that distinguishes the mental disorder of depression from normal mood changes.

The term "clinical depression" means the depression is severe enough to require treatment. Types of clinical depression include major depression, dysthymia, double depression, bipolar disorder, and seasonal affective disorder.

Depressive illness usually begins in adolescence or early adulthood. It is often not recognized as an illness, and thus people who have it may suffer for years without a proper diagnosis or treatment.

People with depression often suffer from the following symptoms:

• Noticeable change of appetite; significant weight loss or weight gain
• Noticeable change in sleeping patterns, such as fitful sleep, inability to sleep, early morning awakening, or sleeping too much
• Loss of interest and pleasure in activities formerly enjoyed
• Loss of energy; fatigue
• Feelings of worthlessness or hopelessness
• Feelings of inappropriate guilt
• Inability to concentrate
• Recurring thoughts of death or suicide
• Physical symptoms, such as headaches or stomachaches

Not everyone who is depressed experiences every symptom. Symptoms and their severity vary with each individual case of depression.

Depression affects approximately 17.6 million Americans each year. The highest rates of depressive disorders are found among those aged 24-44, and the rate of clinical depression for women is about double that of men.

Studies show that depression is the illness that underlies the majority of suicides, is the eighth leading cause of death, and is the third leading cause of death among people aged 15-24. One of the best strategies for preventing suicide is the early recognition and treatment of depression.

Although scientists do not know the exact mechanism that triggers depression, they do know that a serious loss, chronic illness, difficult relationship, financial problem, or any unwelcome change in life patterns can trigger a depressive episode. Also, people with a family history of depression are generally higher at risk.

Depression is one of the most treatable mental illnesses. Between 80 and 90 percent of all depressed people respond to treatment and nearly all depressed people who receive treatment see at least some relief from their symptoms. Psychiatrists agree that severely depressed patients do best with a combination of medication and psychotherapy. Without treatment, symptoms can last for weeks, months, or years.