The mind is an amazing thing. It is also amazing how easily the mind can be tricked into  thinking something is real when it is not. Case in point is the dude in this video who decided to try to ride a virtual roller coaster - standing up. His mind thinks it's real, and the guy can barely stay on his feet - and nearly crashes into his computer.

Apparently your mind knows that roller coasters were not intended to be ridden while standing up.