What's wrong with my cat?

My cat’s been sitting here by me on the couch like he normally does. But when I reached over and started petting him, he jerked away and meowed at me, and he was shrinking away from me.

He’s NEVER like that. He’s the most mellow cat I know. I tried petting him again later and he meowed, this time really loud, and swatted at me.

He’s still napping next to me, and I have no idea why he’s acting like this. We’ve been treating him for some kidney problems but it doesn’t seem like it could be related to that.

I’ll probably take him to the vet tomorrow but in the mean time I’m really worried.

Any cat owners out there know what’s up?