Why do you feel nausea after drinking water?

When you run, your body redirects blood away from your digestive system and into your muscles. It takes a while for your body to realize that you've stopped running and start the digestive system up again (it never entirely shuts down, but it does sort of go into "low gear").

Your digestive system is not prepared to handle anything while it's in "standby" mode, so putting anything into it, even water (if it's more than just a very small amount) makes you feel sick.