Depression is the most common mental disorder in the United States, affecting about 6.7% of the country's population age 18 and older in a given year. According to the newest edition of The Diagnostic and Statistical Manual of Mental Disorders (also known as DSM-5), some of the main symptoms of depression include diminished interest or pleasure in almost all activities, slowing down of thought, reduction of physical movement, loss of energy, and feelings of worthlessness.