Definately check what the temps are in your snake's cage. Most people use under-the-tank heaters instead of heat lamps, but when I set up the tanks for my neice and then my nephew, I ended up using both to get the temps right with a warm side and a cooler side. The under-the-tank heater is better for digestion but the heat lamps warmed the ambient air in the tanks so the snakes felt more comfortable moving around and didn't spend all their time in their hides.
My own snakes are kept in a room that maintains the proper temp range so I don't need special heat sources for each tank (about 100 at current count with more arriving next week).
Just a note: Do be careful driving your snake around during the hot part of the day. I went to college in Louisiana and worked outdoors during the summer there, so I know how hot it can get. Baton Rouge is a little farther north from where I was, but cars can get very hot very quickly. If your snake is in any sort of container in your car, it really isn't getting any benefit from the A/C. Since you said your snake went "belly-up", it was definately getting over-heated. A few years ago, when the Breeders Expo was held in Orlando, I purchased several snakes of various ages. I only had a 1 1/2 hour drive home with the A/C going full blast. I was comfortable and thought the snakes were also. They were in their individual containers, in a paper bag on the front passenger floor. When I got home, 1 snake was dead and 2 others were showing the signs you described. I did my best to cool them, thought they were okay, but both died over-night. The 2 that survived were the ones at the bottom of the bag. The heat from the sun that was partly shining through the window onto the bag was enough to over-heat the snakes.
