An anxiety disorder is a class of mental disorders characterized by chronic and debilitating anxiety. This includes:
Researchers reported in late 2008 that "[u]p to 20 percent of children and adolescents are affected by persistent and excessive worry that can manifest as generalized anxiety disorder, separation anxiety disorder and social phobia." Anxiety can be described as a lack of faith.
Abnormal Psychology, Rosenhan & Seligman, 1984