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Reason I say that is that (while there could be a list of reasons as long as your arm) the vet hasn't found anything wrong immediately and it sounds rather like a post fight stress reaction. They're drained and everything is slowed down and/or muted.
If it's possible (and it might also partly explain the patch on the eye) just keep him in overnight, lots of love and cuddles, taste treats etc. It'll pass within 24 hours although you should keep an eye open for any infections from puncture wounds.