Anxiety Disorder: Introduction Anxiety is the experience of having worry, fear, or feelings of trepidation. Mild to moderate or occasion severe feelings of anxiety are normal reactions to stressors in daily life. Anxiety can manifest in one's mood, behavior, thoughts, and emotions. Although the experience of anxiety can be unpleasant, a normal amount of anxiety can serve to help people to recognize and more effectively deal with stressful situations, such as starting a new job or moving across the country. Anxiety can also be experienced without any stimulus at all or due to a perceived stressor that may not exist, such as a child who is afraid of a monster in the closet at night or a straight-A student who worries about getting a failing grade. If anxiety rises to excessive levels or becomes recurring or continuous, it can develop into a mental health condition, called anxiety disorder. There are many types of anxiety disorders. Anxiety disorders are multifaceted and can be difficult to recognize and differentiate from other medical conditions because they present with a wide variety of manifestations. Anxiety can also be a symptom of many medical conditions in addition to anxiety disorder.