He might be waiting for nightfall or for a fly to go by.... maybe move him to a flower bed where there's some moisture.
It's not hopeful for him though, if you poked him and he didn't move.
Well, I took him down to the stream and when I put him down, he hopped away like normal. So I guess he wasn't as dead as he looked! Still trying to figure out why he just sat there all day. Huh.