Depression (mild or major depressive disorder) is a common and serious medical illness that negatively affects how you feel, the way you think and how you act. Fortunately, it is also treatable. Depression causes feelings of sadness and/or a loss of interest in activities once enjoyed. It can lead to a variety of emotional and physical problems and can decrease a person's ability to function at work and at home. Depression symptoms can vary from mild to severe and can include:- Feeling sad or having a depressed mood- Loss of interest or pleasure in activities once enjoyed- Changes in appetite - weight loss or gain unrelated to dieting- Trouble sleeping or sleeping too much- Loss of energy or increased fatigue- Increase in purposeless physical activity (e.g., hand-wringing or pacing) or slowed movements and speech- Feeling worthless or guilty- Difficulty thinking, concentrating or making decisions- Thoughts of death or suicide- Symptoms must last at least two weeks for a diagnosis of depression.Depression is among the most treatable of mental disorders. Psychotherapy is often used in along with antidepressant medications for treatment of mild & severe depression.