I'd like a bit of advice /an/. I have had a cat for about

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I'd like a bit of advice /an/.
I have had a cat for about 5 years, who lived pretty well with my dog, and lately he's been acting very strange and aggressive. He was always bothered by people yelling and the like and sometimes even assaulted my mother for yelling, but we could pass that off. What's strange is that lately, he has an odd dynamic with the dog - my brother picked her up, and he immediately meowed as if someone was attacking him, and assaulted my brother. It's been small incidents like that, about one a week, and about an hour ago it happened again, way bad.
>Be in bed, reading a book
>Dog comes in the room, making vomiting noises
>Look at her and wait for her to finish so I could clean up
>Cat comes in too, comes up right next to the dog and watches her mouth
>As soon as she actually vomits he lets out a horrific meow and pounces on me, claws the shit out of my arms and getting a bit of my face as well
>Yell at him while trying to fend him off, he calms down and walks away still alarmed, all hairs on end

I had blood all over my arms and face, closed the dog off in a separate room and washed myself, and the first thing I wanted to do was throw the cat away. I seriously thought of actually abandoning him somewhere far away.

I calmed down and I'm taking him to the vet tomorrow, but honestly, what the fuck? He got castrated as a kitten, as soon as it was possible to do so, so it can't be that.

Pls halp.