Any of several mental disorders that fills an individual’s life with overwhelming fear, dread, or worry.  The person may suffer from dry mouth,  dilation of the pupils, sweating, abdominal symptoms, shortness of breath, pounding heartbeat, trembling, dizziness, tightness in the throat, uncontrollable and irrational thoughts, or other symptoms.  The person may be irritable, restless, and have difficulty concentrating.    There are 6 types of anxiety disorders:  panic disorder, obsessive-compulsive disorder (OCD), post traumatic stress disorder (PTSD), social anxiety disorder, specific phobias, and generalized anxiety disorder (GAD).  Although each has different characteristics, a chemical imbalance of serotonin, a neurotransmitter, appears to be a common factor.  Treatments include drugs such as antidepressants, psychotherapy, and behavior therapy.