Gill, is there anything that you can detect in Franta's behaviour that appears to give him any ease at the moment? I think the fact he's drinking, albeit a little, is a positive sign. He may have started to clamp his mouth shut in anticipation of being fed or given medication (cos he's a stubborn little soldja). If he doesn't feel like it at the moment then his jaw lenching could as you say be almost a food phobia.
Could you perhaps try just dampening his gums from time to time and seeing if he relaxes a little? He's obviously feeling better about being home, because he was shouting for you, and he settled ont he bed. Even if he's not actively sleeping as such, having some quiet time may be good for him just now.
Sometimes with Paddy, I would leave him in his cosy little corner, because it was dark, warm and comfortable for him, and other than to check on him visually I would leave him be for a while. You could perhaps try and see if he settles any, just keeping an eye on him to make sure he doesn't collapse in the meantime.
I recall reading once in a book (I think it was a James Herriott book in fact but not altogether sure , as it may have been Buster Lloyd Jones, another good vet of that era) how he was once called upon to euthanise a sheep which had been injured. Instead, he gave it slightly less than was needed, and it went into a deep sleep. After almmost 24 hours, as he was beginning to think it wasn't going to make any difference, the sheep woke up and began to take an interest. He worked on the assumption that sometimes animals (and people) need a period of complete rest in order to heal and that sedation can sometimes be a useful tool in that regard. Franta's had cage rest etc, but it's not been in his usual familiar surroundings, and I wonder if he needs a day or two to "reset" himself?
I say all of this, but I know nontheless how anxiety-inducing it is for you, feeling helpless when you would give your own right arm in an instant to make everything right again.