Anxiety disorders differ from normal feelings of nervousness and involve excessive fear or anxiety. Anxiety in particular also refers to anticipation of a future concern and is associated more with muscle tension and avoidance behavior. These disorders can cause people to avoid situations and places that might cause them to feel trapped, helpless, panicking, embarrassed, and scared. Job performance, school work, and personal relationships can be affected. Anxiety disorder is the most common of mental disorders affecting majority of population. For people who have it, worry and fear are constant and overwhelming. It is a serious mental illness, but proper treatment helps most people lead normal and productive lives.