I've ridden unicyles. They are very safe. You basically only go at a jogging pace at the fastest, and if anything weird happens you jump off and land on your feet.
I want a WhatIf post explaining the optimal size of the loop, the speed required to make the loop, the force required to reach that speed, and what would happen to the ship and its passengers. Also, if we could get some aspect of this approaching light speed, that'd be great.