Why can vigorous exercise make you throw up?

[mitchell]

So I'm not exactly sure how to respond to this experience. I decided to do Track & Field this year for high school, I'm in grade 10. I ran for like a week and a half when the season started, but then I really strained my knee and I couldn't run for about a week. Then I started as soon as my knee was completely painless. So far I havn't had any trouble as far as muscle strain. But after a (hard) practice I threw up. It wasn't like all that graphic or anything. I felt really sick to my stomach so i just kinda waited by a toilet, then I just threw up (yes I made it into the toilet). It wasn't really all that like "bad" either... it could have been worse. It wasn't like the flu sort of throw up, it was more like a spit up... from your stomach. THere wasn't much in it and it was pretty much water, just looked like a giant snot blob. After that I felt a HELL of alot better. Um, I'm not fat, my body fat percentage was like 9% I think.. so not super low, but I think it's pretty healthy. I'm a swimmer, and I'm decent at it. But running isn't as "nice" to your body, especially sprinting. I have never had previous running experience or training.. so that could be a factor. SO my question for you is, what would you do if you threw up after a vigorous practice, but you probably shouldn't have (I feel like I should've been able to take that practice without such extreme side effects). I want to keep running just so that I can get into a better shape which will help me with my swimming.