Clinical depression is a serious medical illness that negatively affects how you feel, the way you think and how you act. Individuals with clinical depression are unable to function as they used to. Often they have lost interest in activities that were once enjoyable to them, and feel sad and hopeless for extended periods of time. Clinical depression is not the same as feeling sad or depressed for a few days and then feeling better. It can affect your body, mood, thoughts, and behavior. It can change your eating habits, how you feel and think, your ability to work and study, and how you interact with people. People who suffer from clinical depression often report that they "don't feel like themselves anymore."