It's peculiar, but I cope much better with foreign heat. In the UK I suffer when it gets hot.
It's a bit humid in England, it could be the heat combined with humidity.
My secret weapon is tomato juice. I've tried fancy and expensive electolyte drinks and I only used one which was any good, but don't know where to get it from. (It was handed out in the Mersey 24 years ago, but they no longer use it)
Tomato juice is cheap (less than 50p a litre for Tesco Value) and easily available. At least use some kind of fruit juice if you can't get tomato. Dilute it if it is really hot. I sometimes carry a tube of tomato puree to squirt into a bottle full of water to make a good emergency electrolite drink. Try tomatoes, you'll be surprised!
Keep drinking too. Don't worry about the drinking too much water thing. You have to be pretty determind to do yourself harm by driniking too much water.
I've cycled through Arizona and Death Valley with the temperature just over 100 (It was spring, not quite as warm as summer) I took a sip, sometimes a very tiny sip, from my bottle at every milepost and had absolutely no trouble from heat. Neither did my friend who was with me and did the same. It could get serious in a place like that. Did get sunburnt pretty bad though because I sweated all my sunblock off my forehead. I started wearing my hat, which stopped it getting any worse.
I love the heat. I wish it was much warmer and am dissapointed with the weather so far this year.