Thanks all of you for your advice. Had to get him a new humidity reader, but it turns out his enclosure is actually less dry than I thought. A little bit under the right level, but it would seem he's much more comfortable than I! It actually makes sense, his vivarium is smaller than the room, it's easier to regulate temperature and such in there.
(And I've heard of snakes soaking before a shed or if the enclosure isn't humid enough...but seeing as Steve never soaks in his water dish, I suppose I might have jumped the gun a little.)
Anyway, after fussing around with heat and moving things around, the temperature gradient is back to normal and the humidity is at a decent level.

I offered him a smaller meal than he usually eats yesterday and he gladly accepted it, so it seems I'm in his good favor again. Phew!
That herp has me on a string. I'm like a nervous new mother.