http://www.nimh.nih.gov/health/publications/panic-disorder-a-real-illness/summary.shtml
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National Institute of Mental Health, National Institutes of Health
Panic disorder is a real illness. It can be treated with medicine or therapy. If you have panic disorder, you feel suddenly terrified for no reason. These frequent bursts of terror are called panic attacks. During a panic attack, you also have scary physical feelings like a fast heartbeat, trouble breathing, or dizziness.