So sorry to hear about your mom.

Seems kind of like seizures with cumulative damage to the CNS. That would not necessarily show up, even on MRI's. Autoimmune cause is possible, the most likely culprits being Sjogren's Syndrome, Lupus and, as one poster indicated, Celiac Disease. Sarcoid too? And, yes, Addison's is a possibility. It can cause neurological symptoms, and although the age of onset is usually earlier, it can occur at any age, and a family history of autoimmunity may be relevant here.

For the sake of completion, check if she's gotten an paraneoplastic panel. She should also be tested for any infectious etiology--some viruses can mess with the nervous system. Also, vitamin deficiencies, especially B12, although her symptoms don't suggest that. Even so, cover all bases.

I'm reviewing here the work-up I got when I was hospitalized earlier this year. My symptoms did not resemble hers, but they were neurologic, and I do have an autoimmune disease, which could be the basis of her problem. Great idea to have her evaluated at the Mayo Clinic, or some other top-notch academic medical institution.

I hope you can get some answers soon. Not knowing is hell. Believe me, I know. Hang in there.