Ok guys, I’ve learned yet another lesson.
Glad you're OK.
As a former flatlander I agree that altitude and dehydration can screw you up big time. The lack of O2 you can notice if exerting yourself .
Dehydration is tougher. The humidity is so low sweat evaporates before your clothes get wet. Plus you lose a large amount of water just breathing. When I lived in the midwest in the heat an humidity I got thirsty. In the mountains for some reason I do not feel thirsty when I should. Its a mystery to me.