An array of abnormal variations in the mood of a person is cause due to depression and anxiety. A person with this condition will get 90% of anxiety disorder develop depression reaction which cause chemical reaction in brain.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. It is often accompanied by low self-esteem, loss of interest in normally enjoyable activities, low energy, and pain without a clear cause. Those affected may also occasionally have false beliefs or see or hear things that others cannot.Some people have periods of depression separated by years in which they are normal, while others nearly always have symptoms present. Major depressive disorder can negatively affect a person's personal life, work life, or education as well as sleeping, eating habits, and general health.About 2–8% of adults with major depression die by suicide,and about 50% of people who die by suicide had depression or another mood disorder.