He goes back to see the vet tomorrow.
He's had these two small hard lumps, one on each side of his head (lymph node or salivary gland?), in the same spot for years and they never bothered him, so I figured it must be okay.
But one side is a little larger than the other one now, not sure if it's the actual lump, or just the area is slightly swollen. The weird thing is, whenever I touch his head anywhere on that side, his head starts to shake or twitch in a way similar to Parkinson's tremors. He doesn't seem to be in pain from it or try to move away if I touch him, it's just odd.
He's eating, drinking and using the litterbox normally and even playing sometimes. I don't even know if those lumps have anything to do with it to begin with.
I also noticed a couple of really, really tiny hard things right under his skin on that side too.