***I figured out the problem before I managed to post this but thought I'd post it anyway to serve as a suggestion to anyone else having this problem. When I got to the last line about not seeing him on his wheel I had a brainstorm and checked. Sure enough, he'd kicked grit into the space between the stand and the spindle and it couldn't spin freely. I bet you anything he'll stop pacing now
First off, I very rarely see the little guy. He seldom comes out before midnight so generally if I want to see him I have to stay up very late and hang out in the dark until I hear him moving around, then I flick the light on. The last couple of times I've seen him though he's taken to this weird repetitive pacing at one of the narrow ends of the tank. He zips back and forth and at each end he does this little jump up and kind of twists back in a semi-flip to head back the other way.
His tank is 36" long by 16" wide and he only exhibits this behaviour along the short sides. All I can figure is that it's because those ends have only one terrain, whereas if he were to pace the long sides he would have to scramble over two different terrains and over the barrier in the middle. His tank is half deep paper-based substrate for burrowing and half sand with a "rock" cave system in the middle. He has a flying saucer but I haven't seen him use it lately.