Cats going crazy

I have a cat that is about a year old and got very sick all of a sudden vomiting, stopped eating after $1000.00 at the vet they couldn't find anything wrong with him.  Advised me to put him down I couldn't do it so I brought him home.  After 2mths he is still eating but broke out from something constantly itchs and has huge sores.  Our vet doesn't want to give steroid shot because of history but we gave tried antibiotic steroid spray and anthesiame.  Today when we came home its like he is losing his mind and is jumping and meowing like he's never done.  Is it possible for a cat to go mad?

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