how nervewracking! i'd think if he continues improving, i wouldn't worry too much, but if he begins staggering more or acts more spacey than before, i'd call the vet asap. the issue with metacam is dose related, and MOST of the time it has to do with multiple doses of it. so hopefully tiggy is ok with it. I took punkin to one vet for accupuncture and that vet gave his own cat metacam. i know some of the high dose kitties that used it because it was the only thing that brought relief. the dose matters.
at least they were halfway right with the convenia - they gave it for a skin issue, which is what the AB was developed for. i suspect you're ok with it too. the risk with it is allergic reaction, and because it lasts 2 weeks in the system if you have an allergic reaction that's a long time to deal with it.
sending the best wishes from our house to yours tonight!
eta - i take anya, my norwegian forest cat kitty, to the groomers for a "Brazilian" every couple of months for that little hygiene problem. just a thought for the future. she only charges me $10 for it.