Just a follow-up to my previous post: I am fairly convinced that it was just the heat which was bothering Shakespeare, and not some dire creeping death. He perked up considerably when a cold front came through ("cold front" being relative, of course!) and is now happy to run around and patrol at night instead of during the day. So I hope he continues well!
He did, however, gain some weight, so now I'm trying to get that off him.... It just never ends, does it?