Something scary happened today, I think I fainted?

I am a 19 year old female, I was on the bus on the way home from shopping, I suddenly felt dizzy and felt like I was going to be sick, I started sweating really really bad (was dripping off my head and neck) and everything turned white for around 10-15 minutes. My head slammed onto the chair infront, I think by this point I was unconscious for a few seconds then woke up to everything being white again for another 5-10 mins, my head and legs felt like lead. Luckily when it was my time to get off the bus I was nearly back to normal but 3 hours later I still feel strange. What could this be?