Since the Seventies, perceptual psychologists have known that our eyes jiggle constantly. These oscillations are called saccadic motion and without them we would go blind with our eyes wide open. If your eyes aren't free to jiggle, you can't see. Psychologists discovered this by holding people's eyeballs still with little clamps. I know it sounds like something from a Marilyn Manson video, but actually, it was done painlessly, on volunteers, and the results were astonishing.
Subjects immediately go blind.
Their visual field turns to gray. The world reappears. The Mind's Eye is similar. Without motion, your imaginary world disappears. At least a little more quickly.