I think you should get the FIP test done to determine if that is what this is or rule it out. A diagnoses sooner is better than later since you would have more time to treat. If the FIP test comes back negative then I would recommend seeing a neurologist.
There isn't just one definite FIP test though and all of this really confuses me. I have heard of the ELISA test and that might be something that tests for all the viruses (FIV, FeLV, FIP...?) I'm not sure about that though.
Otherwise I've read that it's impossible to actually "diagnose" FIP until the autopsy after death.
I'm not sure which tests I should be doing and if they are really worthwhile. If I do have to bring him to a neurologist I'm not sure how much that will cost and I don't know if I'll be able to afford it.
My cat is still the same. He hasn't gotten any better or any worse in the last week. He can't walk right so all he wants to do is lie down and rest or hide away somewhere, but otherwise he looks healthy. He's still eating and drinking. He's never had a fever when I brought him in to see the doctor. He's still urinating in his litter box but not defecating. Every single time he defecates he falls over onto the floor and he would go while lying on his side if I didn't hold him up everytime.
I really don't know if I should just be waiting at this point or doing something.
I wish Briana would come back on here and let us know what happened with her cat...