Unfortunately I also suffer of motion sickness, and I can confirm, barbarosso, that you're not the only one! It is one of the reasons why I could never finish playing Obduction and Quern, sadly... (And working on the tests of my game Myha was terrible for me).
I have never understood why I have motion sickness with these adventure games, because I could play games like Skyrim or Fallout III in the past without too many problems.
It would seem that I have found a link (in my own case) between screen resolution and motion sickness. Playing in 1280x720 is quite ok for me, when the same game in 1920x1080 will make me sick. I don't know why (fps/speed, maybe?).
If anyone has found a way to fix motion sickness in 1st person 3d games, I'm interested!