I was in class today and I began to feel a bit nauseous, I shrugged it off but a little while later my vision began to blacken around the edges and I felt dizzy, I also heard ringing in my ears and had what I could only describe as a cold sweat with no sweat. I also had a permanent purple-ish collection in the center of my vision while this was happening, similar to what I would see if I looked at the sun for a second and looked away. I also could not hear very well. All of this did subside after a little while, but what does all this mean and what caused it?