I drove two cats 300 miles across Pennsylvania in weather like today (85 F and muggy) about three years ago. Despite applying cat tranquilizers to both kitties I got to see the greatest feline freakout I’ve ever seen. Basically an overheated cat got carsick and completely lost it — as in “LET ME OUT OF THIS CAR RIGHT NOW!”

Happened on the PA Turnpike, and luckily there was a very wide pull-off right there. Had the cat on leads as a safety precaution and thus was willing to open the door, hold the cat, and lean him out the door so that he finished vomiting outside rather than on me. He was also yowling and foaming at the mouth (literally) while all this was going on.

Cat then struggled and jumped down. He tried to go under the car, but the lead pulled him up short. So he turned to run away from the car. Right then a semi went by 30 yards away - jake braking. The cat turned and jumped back into the car.

I spent the next half hour cooling off the cats using a bandanna dipped in cool water (wiping down their ears and faces), cleaning up myself and the car, and arranging a spot for the cats that the A/C blasted cooler air on. (Since their previous spot was apparently not cool enough.)

The rest of the trip was anti-climactic from there. The cat that got sick was completely wiped out and basically just complained now and then. The other cat was completely zonked from the tranquilizer and basically moved and meowed at 1/4 speed the entire trip.

Have dealt with moving cats via car 3-4 times. And hot weather is essentially dangerous for them since they easily overheat in a car.