What Causes Blurred Vision And Cold Sweat While Doing Strenuous Exercise?

My daughter is 17, she has on and off over the last few years experienced blurry vision, lightheaded cold sweat on the back of her neck, and I think a slight drop in blood pressure when she does vigerous exercise She plays travel softball and used to only have this at times when it got really hot, but the last two weeks at her pitching and hitting lesson for 1 hr she got had symptoms, especially during hitting where it is fst paced ball after ball