Hi, i used to work at alton towers a few years ago. I recently went about 3 weeks ago. I got together with some of my old colegues and they showed me some new rides including hex and how it works. It is in fact the room that moves. There is also special lighting employed to enhance the effect.
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'