All humans experience fear and anxiety. Anxiety is often accompanied by physiologic changes and behaviors similar to those caused by fear. Adaptive anxiety helps people prepare, practice, and rehearse so that their functioning is improved and helps them be appropriately cautious in potentially dangerous situations. Maladaptive anxiety causes distress and dysfunction. As anxiety increases, performance efficiency increases proportionately but only to an optimal level, beyond which performance efficiency decreases with further increases in anxiety.
Anxiety disorders are more common than any other class of psychiatric disorder.
However, they often are not recognized and consequently not treated. The causes of anxiety disorders are not fully known, but both physiologic and psychologic factors are involved. Psychologically, anxiety is viewed as a response to environmental stressors, such as the rupture of a significant relationship or exposure to a life-threatening disaster. A person's anxiety system usually makes appropriate and imperceptible shifts from sleep through arousal to anxiety and fear. Anxiety disorders occur when the anxiety system operates improperly or, sometimes, when it is overwhelmed by events.