I to have panic attacks that come from nowhere. I must say that the first step that I took was recognizing the feeling before they came. When you can start feeling them coming, then you can start to realize that it's only a "panic attack" and you're not going to die. I'm not going to say that it's easy by any means because I know how they feel. But, once you can realize the oncoming, and learn to deal with it accordingly...It will make your life easier.
Another thing is, (at least for me) watch my diet, and by diet I mean something that would trigger and attack. Start thinking about what you've had to eat or drink prior to the attack. Be it food, drink, or smoke. Some of us are just more vulnerable than others.
Good luck, and please let me know how it turns out