I grew up in Hattiesburg in my mid-teens, walked 36 holes a day just about every day in the summer, changed shirts at lunchtime, drank water like crazy but it really didn't phase me.
I go back now to my in-laws house, walk outside, take one breath of air and say, "I might can go 9..."
I know what you mean. It's even worse when you start getting away from the Coast, no gulf breezes to help. I practically suffocate when I visit relatives in Vicksburg.