Your description of his behavior is very close to what happened to Sterling after one of his vaccination. We discovered him the next morning huddled down in the closet, unwilling to move, with a fever. We took him to the vet, who gave him an injection (possibly metacam), and by the next day, he was pretty much back to normal. But we thought he was dying at first!
Metacam can cause kidney failure in cats, and once a cat has had the one time metacam injection, I'm pretty sure, should never ever have metacam in any form, again.
I know many will disagree with me. But I am one of those who is against metacam use in cats.