@keizo he was throwing up and not eating. Last week, he spent a night at the vet, on a drip (to rehydrate). They gave him medicine for pain and vomiting. Since then he is better, but only eating a little and not playing at all.
@pme hope the op went well! It's crazy how much he was missed. I'm quite used to very independent cats, and the rescue centre said he wasn't very sociable. But he loves being with people. Thankfully just one night at the vets.