Anxiety disorder is a blanket term covering several different forms of a type of mental illness of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry near the end of the 19th century. Gelder, Mayou & Geddes (2005) explain that anxiety disorders are classified in two groups: continuous symptoms and episodic symptoms. Current psychiatric diagnostic criteria recognize a wide variety of anxiety disorders. Recent surveys have found that as many as 18% of Americans may be affected by one or more of them.

The term anxiety covers four aspects of experiences an individual may have: mental apprehension, physical tension, physical symptoms and dissociative anxiety. Anxiety disorder is divided into generalized anxiety disorder, phobic disorder, and panic disorder; each has its own characteristics and symptoms and they require different treatment (Gelder et al. 2005). The emotions present in anxiety disorders range from simple nervousness to bouts of terror (Barker 2003).