In my opinion, you can feel that you are moving, but I could not tell I was spinning. I get motion sickness if I read or watch a movie in the car or a plane. I did not get sick from M:S. The first time I rode it, I felt almost a bit drunk. But that wore off within a couple minutes. The next time, I felt no effects.
You just have to heed the advice.
Keep your head back, against the headrest.
Look directly forward, at the screen.
DO NOT CLOSE YOUR EYES. (You will then feel the spinning)
DO NOT LOOK LEFT OR RIGHT.
I like to add "relax" to the list. It is a great ride. But you will never enjoy it if you are too wrapped up in what it has done to other people. No one can predict what it can do to an individual at any given time.
Ted