Dave,
I'm not an expert, but unfortunately, experienced, and it is serious, and after the first time, it seemed to be easier to be negatively impacted by excess heat.
First time for almost heat stroke, was as a teenage unloading boxcars in mid summer.
Last time was 12 or so years ago ...company golf outing, attendance pretty much required....didn't finish that round.
Joe described to a "T" the symptoms for heat stroke I had every symptom, but the stroke, I think...and if you get there you are already in trouble.....If you get to heat exhaustion, stop, get water, get in front of a fan, get in the house if it is cooler, ask your spouse to keep an eye on you.
When I was young, salt tablets were recommended....they just made me nausious....
Thank-you to guys who answered Dave's question....I got more knowledge too.
Be careful....it is very serious