Blackout in vision after exercise?!?!?

Today in conditioning (weight lifting cl) we worked out for the first time this semester in the weight room. It was the first time ive worked out in awhile but it wasn't overly hard or anything. Anyways after the workout when i was standing up my stomach started feeling weird and i suddenly felt hot and cold at the same time. since i couldnt sit down(one of the rules while in the weight room) i started feeling unbalanced and i felt like i couldn't move along with the other symptomes. It was after this when a ring of black appeared around my eyes and it eventually spread until i couldnt see at all. During this time i could still hear perfectly clear and felt everything fine but i just couldnt see and i felt extreamly dizzy by this point. When i was finally guided to a bench by a friend my vision started clearing up again but i still didnt feel right for about another 10 minutes. Im a sophmore in high school and play a couple sports and i've never had this happen to me before and im actually pretty skinny and in good shape so i have no idea why this happened. If anyone can help me out with this i'd really appreciate it. Thanks.