It's useful to add that, generally speaking, when you get the motion sickness the effects can be intense. I found out the hard way that even if you've never suffered from motion sickness via regular vectors (car rides, boating), you're not immune.
I've only had one bad experience that resulted in motion sickness - during and following an extended play of Half Life 2. The feeling stuck with me for several hours, to the point where I couldn't even look at the TV screen from the couch.
It was a miserable experience; afterwards, I was careful to never ignore the signs, and stopped playing any demo that started to feel just a little 'off.'
Something like this could be a platform-killer and doom your project before it ever reaches critical mass.