I suspect it was a stress reaction to a large new burrow-style cave I'd put in his tank earlier this afternoon, because I took it out and he's stopped trying to get in his water dish and has actually laid down on the warm part of his carpet (to dry off, I suppose). But if it was a reaction to the burrow, why now instead of 6 hours ago when I first put it in? He was having a grand time exploring it when I first put it in, climbing all over the top of it (but not going inside yet). Why would he suddenly become so terrified of it he'd rather drown himself than walk past it to hide in his other cave?
For other background info, he hasn't been eating well for about a month now, only a couple worms each week. I tried feeding him crickets this afternoon (before putting the burrow in) and he wouldn't have anything to do with them.
I think after I've given him a few more minutes to calm down, I'm going to re-arrange his tank like it was before with both his old caves and see how he does with that. Any advice on what to watch for/what else to do/what not to do?
For reference, here's the new burrow I put in his tank: http://www.t-rexproducts.com/products/v