Is something wrong with me . . . ?

yesterday during my self defense class, i had another fainting attack; well an almost fainting attack. I was punching the pad and got really dizzy and weak and had to go sit down. after sitting for about half an hour i finally ready to rejoin the class. it was as if nothing happened but it was still embarrassing. i was wondering if i have any sort of disease like a shortage of iron or something :s