If you have ever had a panic attack, you most likely can relate. More often than not, due to the intense experience one undergoes during their first panic attack, one then fears having another.
This fear of having another panic attack is really just a fear of experiencing bodily sensations many associate with fear - rapid heartbeat, sweating, dizziness, difficulty breathing, tingling in the hands and feet, etc.
Unfortunately, the more you fear panic, the greater the likelihood that you'll panic.
Remember this reality that panic disorder is just fear of fear. It might put things in perspective. If fear can't really hurt you, than fearing fear is certainly unproductive.
Follow this link for more on panic attacks and how to resolve them.