Hello, My sone has been swimming for 9 years, he is 12 now. Recently we have him in a water polo type swimming session. Two sessions in a row, he is unable to continue to swim after 30-40 minutes. He says he feels dizzy, and get nauseous. He then start to vomit and cannot keep anything down. Even water makes him throw up. Short of being a virus, which he already had, what could it be?