Panic Disorder

Panic disorder, also know as anxiety disorder, usually consists of brief episodes of intense fear and may occur with multiple physical symptoms. Sometimes they can happen repeatedly and unexpectedly in the absence of an external threat. These panic or anxiety attacks are believed to occur when the brain's normal mechanism for reacting to a threat is aroused.
Often with panic disorder people also feel anxious and worry about having another panic attack. They may avoid situations in which they think that an attack is likely to occur. Anxiety about another attack, and the avoidance it causes, can lead to disability in panic disorder. 
In the United States, 1.6 percent of the adult population, or more than three million people, will have panic or anxiety disorder at some point in their lives. The disorder typically begins in young adulthood, but older people and children can also be affected. 
Women are affected twice as often as men. While people of all races and social classes can have panic disorder, there appear to be cultural differences in how individual symptoms are expressed.