Not a doctor, but dizziness can be one of the most frustrating things to treat cuz it can be caused by so many things, and most of them are not able to be diagnosed by a simple bloodtest. Oh, maybe its your eyes, your ears, your brain, your BP, etc.
Though not a MLB pitcher, my wife just went through a period of constant dizziness for about two months. Many tests and $$ later, we know dozens of things (tumors, fluid etc) that weren't causing it, but have yet to figure what actually was. Every doctor thought they had found something, but then it would later be ruled out. She gradually got rid of it but it was very disturbing to her to have to live and go on w our normal 3 kid life like that almost constantly for two months.
Now just imagine hurling the force of your whole body forward while balancing on one foot trying to hit the corner of the plate w a 90 MPH fastball while having that condition. Sucks to own him for sure. Sucks even more to be him right now.