What Causes Dizziness And Fainting?

I was at the mall, I started getting really hot and thirsty. We had stopped and while we were standing there I got really dizzy. All I remember is everything going dark then boom. I heard my name and tried opening my eyes but everything was hurting. After awhile I stood up and left. (This was yesterday) Now my neck/upper jaw (beneath my ear) is hurting really bad, especially when I stretch, turn or try doing a sit up (in PE class.) Please help me, Thank you very much. Sarena