I think there're all kinds of motion sickness. For example, I can't read while riding in a car. That makes me motion sick. And I can't do anything that spins me around and around and around--total motion sickness there, and hours to recover. I dislike being jerked around on a ride, but I can't really say it makes me motion sick, just uncomfortable.
FoP is a very smooth ride. It swoops and banks. And you're wearing 3D glasses. None of these things bother me at all. I've never even been somewhat motion sick on this ride, however, my DH can't ride FoP. He gets immediately motion sick on it. He thinks it has something to do with the visual effects and the progressive lenses in his glasses, but we're not sure.
OP, if you're concerned about motion sickness on FoP, take a bonine ahead of time. If you do feel bad on the ride, close your eyes. This works for most people since the vehicle itself moves very little. But this ride is so so so worth it. The best ride at WDW, imo. Amazing and beautiful. Leaves Soarin' in the dust!