It's strange seeing this thread because I had one the other day and it is still on my mind. It was especially bad because I was at work. I was supposed to be looking at the computer, papers and files and there were sections that I simply could not see. I could look at a page and I knew writing was right in front of me, but it was too "swirly" to see anything. I ended up walking around for a while, chatted w/some coworkers about it, I was like I swear I am not drunk lol. After about 20 minutes, my vision returned to normal. It is like whatever it was just made its way around and then left. I did have a headache afterwards, not a really bad one though, and a headache the following morning. They never really got bad though.
I have had this happen off and on for about 2 years, and it freaks me out every time it happens. Before yesterday, it had been a couple months. I see the flashy lights, zigzags etc... I would kinda describe it as a kaleidoscope at times.