Depression

Everyone experiences sadness at times. But depression is something more. Depression is extreme sadness or despair that lasts more than days. It interferes with the activities of daily life and can cause physical symptoms such as pain, weight loss or gain, sleeping pattern disruptions, or lack of energy.
People with depression may also experience an inability to concentrate, feelings of worthlessness or excessive guilt, and recurrent thoughts of death or suicide.
Depression is the most common mental disorder. Fortunately, depression is treatable. A combination of therapy and antidepressant medication can help ensure recovery.
Adapted from the Encyclopedia of Psychology