Trix- I"m sorry that this has become worse 13 hour drives aren't generally fun to begin with. A couple of ideas...i hope they're helpful. I bought some off-brand (Walgreens) arthritis heat wraps. They don't get as hot as the name-brand ones, which were way too hot for me. and they seemed to stay hot for about 6-8 hours. That way you can have some relaxing heat on the drive. Another thing I found at walgreens was a memory foam neck pillow.... you know, the ones shaped kinda horse-shoe like? I always travel with one when I have to travel. Keeps my head from flopping around if I doze off. Finally, some pillows for under your arms to support them.

Oh- would it be possible to schedule a massage (if they help you) for when you get to your destination?

I hope the drive is easier and less painful than you anticipate.