Thank you for all the good thoughts, and thanks to Phred for the link.

I never got back to sleep, he asked to go out every 15 minutes ever since then. It's weird though -- he is so miserable outside, but then when he comes back in he is bouncy and wants to play.

We just gave him some Pepto, so hopefully that will settle his tummy soon!\

Edit to say that I am planning on calling the vet when they get in, to see what they advise.