Major depressive disorder (MDD), also known simply as depression, is a mental disorder characterized by at least two weeks of low mood that is present across most situations.[1] It is often accompanied by low self-esteem, loss of interest in normally enjoyable activities, low energy, and pain without a clear cause.[1] People may also occasionally have false beliefs or see or hear things that others cannot.[1] Some people have periods of depression separated by years in which they are normal, while others nearly always have symptoms present.[2] Major depressive disorder can negatively affect a person's personal life, work life, or education, as well as sleeping, eating habits, and general health.[1][3] Between 2–8% of adults with major depression die by suicide,[2][7] and about 50% of people who die by suicide had depression or another mood disorder.[8]