Sudden fit of nausea and prolonged headache?

So today during second period, we were all standing in a huge circle, like every day. Suddenly I started sweating like crazy, I felt really dizzy and weak and my stomach clenched. I felt and looked like I was going to vomit. This lasted for about 10-25 min, but I thankfully did not throw up. Since then, I have had a MAJOR headache and I passed out when I came home from school. Not literally but I fell asleep. My head is still hurting, and I've had like 3 bottles or 2L of water so it isn't dehydration. Am I sick or something? My mum has been experiences almost identical symptoms.