Interesting answers, when I went on the Hex, I had a camera on a string and I can confirm that the seats do move, but by approx 10 degrees, the rest is an illusion brought on by the room spinning and your eyes seeing one thing but your body another.
The result is the brain is confused as the two sense give conflicting advice and you feel dizzy. This then makes you think you are spinning.
From a safety point of view the restraints are simply inadequate for you to be 'turned upside down'