It's the first time I've ever seen heat exhaustion before, and I certainly wouldn't have suspected it on so mild a day. Without the info identifying what was wrong, we probably would have just left him alone, hoping he would recover. God only knows what sorta damage that might have caused. My sister is going to take him to the vet in a couple days just to make sure he's hunky dorey, but aid was applied so quickly that I'm sure he's probably fine.
On a sidenote, I've now got a giant tub of codeine in front of me. It's supposedly enough to kill 14-28 people. Hmmm....