Once someone has had a panic attack, he or she may develop irrational fears, called phobias, about the situations they are in during the attacks and begin to avoid them. That, in turn, may reach the point where the mere idea of doing things that preceded the first panic attack triggers terror or dread of future panic attacks, resulting in the individual with panic disorder being unable to drive or even step out of the house. If this occurs, the person is considered to have panic disorder with agoraphobia.
Panic disorder is a diagnosis given to people who experience recurrent unexpected panic attacks— that is, the attack appears to occur from out of the blue. The term recurrent refers to the fact that the individual has had more than one unexpected panic attack. In contrast, expected panic attacks occur when there is an obvious cue or trigger, such as a specific phobia or generalized anxiety disorder. In the U.S., roughly 50% of people with panic disorder experience both unexpected and expected panic attacks.
Hyperventilation syndrome may occur when a person breathes from the chest, which can lead to overbreathing (exhaling excessive carbon dioxide in relation to the amount of oxygen in one's bloodstream). Hyperventilation syndrome can cause respiratory alkalosis and hypocapnia. This syndrome often involves prominent mouth breathing as well. This causes a cluster of symptoms, including rapid heart beat, dizziness, and lightheadedness, which can trigger panic attacks.
People with panic disorder often worry about when the next attack will happen and actively try to prevent future attacks by avoiding places, situations, or behaviors they associate with panic attacks. Worry about panic attacks, and the effort spent trying to avoid attacks, cause significant problems in various areas of the person’s life, including the development of agoraphobia (see below).