Heatstroke

I can offer a little advice you need to take him to the Vet or give him an IV! What happens is after the extreme heat exhaust the muscles are breaking down and the kidneys are filtering all that muscle and they get over worked and shut down so the dog has to have plenty of fluids to flush the kidneys. Like you said forcing water or whatever in him is not giving him enough fluids to keep the kidneys flushed hence the IV. I know this because I had the same thing happen to me a month ago IV for three days and complete rest dog came through it like a champ. I hope this info helps you bud.