Severe Cat Behavior Issues HELP!?

I've been around cats my whole life and I have never heard of such bizarre aggression, not even from the most wild ferrals that have to be put down. I really don't know how to advise you in this, except to continue consulting with your vet. Please be careful and protect your other pets from this one until you have found the solution. I will take a WAG at this however. Is there any chance at all that this cat is is experiencing constant internal pain?