It's heat stroke.

Had it many, many times unfortunately - for whatever reason, my body doesn't cool off properly. At least you can sweat - but watch for dehydration.

I find what helps most is drinking soda water - there's extra minerals and salts to help you keep hydrated.

Crank up the A/C too if you have it, or have a fan run right on you.

If you have episodes of vomiting get to a hospital, but otherwise, just take some cool (not cold) baths or showers to cool down too.