Panic disorder is one of the so-called anxiety disorders and is the result of an increased level of anxiety which is caused by a change in the way a small organ called the Amygdala, in the brain, responds to anxiety-provoking thoughts or situations.
When this process becomes disrupted, the sufferer develops feelings of anxiety which may escalate into panic attacks or Panic disorder.
Panic Disorder has such diverse and sometimes extreme symptoms. BUT, this is caused by the same internal mechanism in every single sufferer. The brain thinks it is behaving normally as it has become re-set at a higher than normal level of anxiety due to a catalyst of some sort; the catalyst is unimportant actually, what is important, however, is that an internal switch, which activates the anxiety response in the brain has been 'adjusted' to a higher level of anxiety and it is this that causes and perpetuates the Panic Disorder. I don't like the term disorder, it suggests illness and anxiety isn't an illness, it's a natural device that can become disturbed.