I'd be careful on Mission:Space if you are prone to motion sickness. My dh was definitely ill and could barely move for about 4 hours after doing that ride, and he did follow the instructions very carefully about keeping his head back and only looking at the screen and took a Bonine that morning. He had a bad headache, severe nausea, and tingling arms. He basically sat on a bench the entire time the rest of the family did the World Showcase. He says that he has no one to blame but himself, because he knew that he was prone to motion sickness and should have listened to the warnings. He also told me that he was very aware of the spinning. Take off felt like spiraling up to him.
I rode it the following day as well, and I tried my hardest to feel the spinning but couldn't. I only felt the pressure. I think it's just biological for some people.
Beth