I have had a similar issue with driving because I was in a car accident in 2007. What I have done when I feel I am going to have one is find a safe place to pull over for a while untill it passes, but you can not always do that on a freeway. Try taking deep breaths to calm yourself. It could also be helpful to talk to someone professionally about why you are having the panic attacks in the first place. I mean god forbid that you start having one, and it causes an accident. Hope this was helpful. Good luck to you.
I would just drive a lot. Then when you get scared remember those times when you were scared and nothing happened. It also may help to know the statistics such as hours driven all around the country per day or number of drivers to amount of car accidents.