[cypher]

The symptoms you're seeing are very similar to torpor but it does seem unlikely, nothing you've added really suggests that torpor may be likely. It doesn't sound as though he was showing any obvious signs of ill health previously either which does make it really hard to get any idea what the issue might really be without a good vet to check him out.
I'm really sorry but I don't know what to suggest. you can't really do much more but if he is still like this in the morning then I would get him to the vet & see what they say.