Our lab got too hot last spring while playing and suffered what I think was a mild heat stroke similar to what you are referring to. We got him into the house to cool down and drink lots of water.
I limit the amount of play time with our lab during summer months for that exact reason. I throw the ball maybe one or two times for him when its hot out and that it. No more. I put it up. Now if we are around water, I will let him retrieve a bunch. But even the local lakes are so hot right now that it doesn't do a very good job of cooling him so a person needs to be careful.
We have a kids swimming pool set up in the shade for him in the yard that he regularly jumps in to cool off (This works very well for him). He just isn't designed very well for this GA heat.
Black Labs Matter.