Hello, welcome to Just Answer. I will try to answer your questions and help Milo. Are you able to wake him up at all or is he completely limp and non-responsive?
Ok, thanks for the added information. If he has been extremely active and hot, he may just be exhausted and warm. Puppies will often play extremely hard and wear themselves out. You can try moving him to a cooler area or placing a fan in the room to help him cool off. Has there been any vomiting or diarrhea?
I think it would be a good idea to just keep an eye on him, be sure he has access to lots of fresh, cool water, and I suspect in a little while he will be back to his normal self.