Panic disorder: An anxiety disorder that is characterized by sudden attacks of fear and panic. Panic attacks may occur without a known reason, but more frequently they are triggered by fear-producing events or thoughts, such as taking an elevator or driving. Symptoms of panic attacks include rapid heartbeat, strange chest sensations, shortness of breath, dizziness, tingling, and anxiousness. Hyperventilation, agitation, and withdrawal are common results. Panic disorder is believed to be due to an abnormal activation of the body's hormonal system, causing a sudden 'fight or flight' response. Treatment involves cognitive behavioral therapy, using exposure to effect symptom reduction, and use of medication.