That sounds a lot like me in August last year!!
I also booked this trip, two and a half hours away from home - booked hotels, tickets for a water park (kids really wanted to go there). When the day came, I just wanted to die. The night before I just called my husband to our bedroom, locked ourselves in there and told him I was feeling like shit, I was simply having a permanent panic attack - it just wouldn't go. He brought my boxing gloves to try and get the stuff out of me (sounds funny now, but it does help sometimes, just punch, punch, punch) - but it didn't work that time. I just wanted to give up there and then - BUT, I didn't want to disappoint my kids. This is the day I did this drawing http://anxiousiwas.wordpress.com/2011/1 ... g-trapped/
It took me a very long time to manage to get to sleep, and I woke up with the same panic attack - sweating, shaking, that rush of adrenaline going around the whole body, the world seemed like a completely different place, dizziness, pressure on my head, I felt horrible. But I did go. My husband drove all the way (I couldn't get on trains either - worse than cars for me).
The hotel was a "theme hotel" - for kids, you see? - and all the decorations in there made it feel much smaller than it probably was. I felt like I was trapped in there. I felt horrible most of the time. I felt more or less ok when we were at the water park itself - swimming is one of my favourite things, so that was ok. Not great, but ok. Meal times were awful, the restaurants were packed, crowded and I just wanted to run away from myself, and from there. But I stayed there for the kids.
I also remember that I was terrified of the dark at that time (panic brings more panic, which brings more panic... and it goes on) so night time was awful too. Darkness was just the icing in the panic cake.
After I endured a second day there, I asked my family if it was ok for us not to sleep there a second night. They were all ok with that. We stayed at the water park all day, and left before it got dark. (I wanted to get home before night time).
Kids were happy that they went to the water park, they didn't mind leaving a bit early since the beds were not that comfortable, and breakfast was bad too, so we didn't miss much.
That was the LAST panic attack I had in my life. Since then I have been recovering really well. I do have a GREAT therapist, and it helps that my family is also great. I have always explained to my kids how I felt, so they know how things are when I had panic attacks, or when I couldn't do this or that. I still can't do everything, but I can drive now, I can go in lifts, I can go to the theatre, crowded places are not a problem anymore. There are still bits and bobs that I need to work on (such as plane and train travel, drive long journeys), but I am getting there.
I would say that the way to cope when you are in the car is: when you feel a panic attack coming up, breathe slowly, concentrate on what's reality in front of you (your husband, kids, the car, the road) and KNOW that the panic/anxiety is going to go. Let it come, don't try to fight it, don't try to make it go away, because that is what causes it go grow. If you let it come, and become as bad as it can get (you will survive, and it will get to a point where it won't get worse), then it will go. It may come back quite a few times, but if you do this every time, it will become less and less powerful. BELIEVE ME - this works. The hard thing (and hard here sounds like a really weak word) is that we need to go through it. There isn't one thing that will make it go away instantly, unfortunately. You do need to face your fear, but with the right attitude.
I would recommend a website for you to have a look at, where there is a lot of information about this problem and how to overcome it. The address is:http://www.anxietynomore.co.uk/
I really hope this helps! I know exactly how you feel right now.
Feel free to send a private message or reply here asking any questions you may have.
I am getting out of this, and I am sure you can do it too.