I got 10 piercings done in one day before. Granted none of them were nipple piercings, they all hurt in different ways with different degrees of pain but not too much to make me feel nauseous or even lightheaded. I was nervous because of the number of piercings I was getting but once it was over, I felt great. You should be fine. Just try your best to relax. And let the person piercing you know if you feel nervous. They're used to that sort of thing and should be able to calm you down.