Thank you all so much for your kind words and advice.
Fuzzy seemed quite a bit brighter when we picked him up from the vets - he had had fluids and food, and the vet has given us syringes of water with probiotics and liquid food. I have been giving them to him each hour - his breathing is better, no longer clicking and gasping, he has moved about a bit and has even been nibbling straw, has taken the odd pellet from his food bowl and has eaten a piece of cucumber. The only problem is that he seems to get stressed when I pick him up and that makes him pant a bit afterwards, but I need to do it to get the fluids down him. He is also resting a lot but not so lethargic.
I'll feed him again before we go to bed, and again in the night, then in the morning, and OH is going to come home from work to feed him and check him at midday.
Then back to the vets in the evening.
But fingers crossed he does seem to be perking up. The vet has also given us a decongestant to sprinkle on his food once he starts eating a bit more. I think leaving him with the vet today has made a difference - I don't think he'd still be with us if we had left him at home this morning.
Do you think he is on the mend?