Damage to the left parietal lobe can result in what is called "Gerstmann's Syndrome." It includes right-left confusion, difficulty with writing (agraphia) and difficulty with mathematics (acalculia). It can also produce disorders of language (aphasia) and the inability to perceive objects normally (agnosia).
All of those things are quite possible with any disease or injury affecting this portion of the brain and the worst part is that you do of course retain your intelligence while all these things are happening beyond your control.
Very, very difficult stuff. I’m not a religious person but I do send my sympathies to those diagnosed with these things.