After exercising, I feel faint?

i had gym cl this morning and i ran hard! we did an agility run. I had breakfast though and i have gym first period ( 8:51 -10:10). i sat out for a little bit because i was seeing faint things and feeling dizzy I also became very plae. 2nd period i got a little cold and my hands were shaking, i regained some colour but i was still dizzy. and now at 6:30 i still feel dizzy. Some people told me it could be over excursion. I don't know b/c im in sports about 4 or 5 times a week if not more