A panic attack is an acute period of intense fear. Panic disorder is characterized by intense fear of panic and preoccupation with having future panic attacks, leading to decreased overall functioning as one alters life in efforts to prevent additional panic attacks. Just about everyone will experience a panic attack at one point or another but only 2 to 3 percent of the population meet criteria for panic disorder. What distinguishes these two groups is that for the first group of people, a panic attack will be experienced as extremely uncomfortable as it is occurring but once it is over limited attentional resources will go to contemplating the attack. For the second group, the panic attack will also be experienced as extremely uncomfortable as it is occurring. And once the attack is over, their brain will continue to scan for any sign of a future panic attack. This ongoing scanning for any physiological warning sign of a panic attack only increases anxiety, making it more likely that another panic attack will in fact occur. Hence setting in motion a vicious cycle of scanning for anxiety and then experiencing more anxiety. Research has shown that the best predictor of who will develop panic disorder is one’s level of anxiety sensitivity. In other words, individuals who have panic disorder are extremely sensitive and intolerant of the physical experience of anxiety. And the more one attempts to not feel anxious, the more one feels anxious. Panic disorder is therefore known as a fear of fear.