Sorry, that happened to you, John. It's easy to get absorbed and get ourselves in trouble. I was just shooting an old farm by myself in the middle of Summer. No one was around but me. I was out in the sun for two hours and didn't realize I was overheated. I nearly collapsed walking back to the car. Fortunately, a woman came by to walk her dog and I asked for help. (How embarrassing!) She gave me two bottles of water which I quickly dispatched. I'm not as young anymore as I think I am.
At least I got a nice shot. That could have been my epitaph: "But He Got the Shot"