A panic disorder will generally lead to a panic attack, but science hasn't really established what causes the attack. The attacks seem to occur when specific sets of conditions come together, but what makes them puzzling is that the kinds of symptoms experienced by different people before the attack vary greatly.
Panic attacks will happen when someone is anxious or extremely fearful. The biological string of events seems to be the same. The person under attack will experience a typical reaction of extreme fear - the same thing that would happen if they were faced with a real, physical threat. Their heart will beat faster, they will sweat, and they will tremble and be short of breath. Only there is no physical threat that leads them to react this way.
