Well, at least now I can stop wondering whether Oscar was hibernating. No idea why he got sick, whether it was something I did or didn't do, or whether there was anything I could have done, but this morning when I got up, Oscar had died.
Sushi is poking around the corners of the tank wondering what's going on.
I'll probably look for a new snail after I get back from next month's trip. Now, before going away for over a week, seems like a bad time!