Are you sure you're getting enough salt?

That's a perennial issue for me, as I've mentioned before. When I'm borderline hyponatremic, first thing that happens is I pee all the time to try to concentrate sodium in my blood, next thing is I get so nauseous I can't drink water. What you're describing sounds EXACTLY like what happens to me when I go into a ride/run balanced, but don't get enough salt during the exertion or immediately after.

Typically people sweat out 500-1000 mg sodium an hour during exertion. Sodium is the one mineral that humans can't get from plant and animal foods and MUST supplement.