Panic disorder is characterised by discrete episodes of acute anxiety. The onset is usually in the early third decade with often a chronic course.The panic attacks occur recurrently every few days.there may or may not have any underlying generalised anxiety disorder. The episode is usually sudden in onset, lasts for a few minutes and is characterised by a very severe anxiety. (Ref: a sho textbook of psychiatry, Niraj Ahuja, 7th edition, pg no.90)