I went for a run along the Tay at lunchtime - a nice easy 4 miles. It's October, it's Scotland and it's raining so the river is quite full at the moment and the wee path I run along was right next to the water. The Tay is a big river (I think it has the biggest outflow of any river in the UK) so as I ran along half of my field of view was the river. I was running downstream at almost exactly the same speed as the river so the right half of my field of view was moving past me as normal when you run, whereas the left half appeared to be stationary. It was quite a strange sensation.
After a couple of minutes I started to feel decidedly queasy, I think due to my wee brain getting confused by half the world moving and the other half not moving as I ran. After a mile and a half I pulled away from the river and soon felt fine.
In the ultras I've done I've usually started to feel a bit nauseous after about 35 miles, though I seem to be coping better with it each time, and presumably it will be something I'll get used to as I do more and more. Maybe now I've discovered a way to try and get used to running while feeling queasy without having to run 34.9 miles first to create the sensation.
I suppose the alternative would be eating 6 cream cakes before going running - that might work.