I'm glad someone took the trouble to visualize this. I've been having them too (luckily without any headache / migraine), but I was wondering what it was. It's very annoying and disorienting.
I'm glad I have something to show people, as it was really tough to describe.
Thanks!

And for some more twisted downhilling on little wheels, check this mental guy!
http://www.youtube.com/watch?v=LWLbu1wIIEo

This is actually very common in the european Alps. You find these at a lot of slopes.