Cozie, you are kind to ask. Bless you.
I would describe him as sad, depressed even. He's eating the bare minimum, maybe a tablespoon worth twice a day. Sometimes a little extra at lunch time. He's not in pain, he is eating his tablets. He's lost weight in a week he was 8 kg before, but then that's to be expected he's not eating anywhere near what he was before, even without being topped up next door and with various wildlife in the day.
No interest in leaving the house, or venturing upstairs. He's not as vocal, sad little meows now, doesn't say hello when he sees you. No tail up, but will bump my leg with his head when I'm cooking. Just doesn't want any food if he's offered.
His back leg is definitely paralysed from the knee down. He can't feel a thing in it. When he's asleep you can poke between his toes and he won't wake. But brush against a hair anywhere else and he wakes and looks. When he's hobbling about the paw is upside down and being dragged. His pads are pink, and there's heat in it, but still no feeling obviously.
Maybe the vet was right to offer to pts as soon as it happened.
On the plus side he has managed to jump up onto the sofa by himself, have a snooze, and get down again. It's ungainly and you'd nearly think he was embarrassed if that makes sense.
Weirdly, he also seems to have the cold. Sneezing a lot. That's reminded me to look at his meds and see if that's a side effect.