Excessive anxiety and worry, that occurs more days than not and persist for at least six months, constitute the core features of Generalized Anxiety Disorder.  The worry and anxiety feels difficult to control and is about a number of different things.  In addition, physical symptoms such as restlessness, fatigue, difficulty concentrating, irritability, muscle tension, and disturbances in sleep plague the individual.   Social and occupational functioning are significantly impaired. 

American Psychiatric Association: Diagnostic and Statistical Manual of Mental Disorders, Fourth  Edition, text Revision. Washington, DC American Psychiatric Association, 2000.