I am writing this in case it helps anyone. I was diagnosed with auto immune Hypothyroidism in 2004. Since then I am unable to tolerate the standard medication, thyroxine. I have deteriorated with progressive muscle weakness and stroke like/ paralysis episodes on my left side. I was recently diagnosed with FND by a Neuro which I do not believe I have.
During my years of research I have read countless thyroid patient stories whom many suffer the same kind of symptoms of FND. These same symptoms disappear when the patients are fully optimised on meds. From reading, it seems that adrenal fatigue from long term illness or stress can result in these symptoms. Just for your information, if you have had your thyroid tested and told by your doctor that the results are normal you can still have Hypothyroidism as the tests are controversial.
Also, since being diagnosed with FND I have been reading and researching and came across Hypo and Hyper- kalemic Periodic Paralysis. It seems to have similar symptoms and many patients were misdiagnosed with Conversion disorder/FND beforehand.
One last thing, my Endocrinologist has suggested I could be suffering from Hashimotos Encephalopathy ( or Steroid Responsive encephalopathy as it can also be called ) so I have researched this lately. It also presents with the same symptoms and guess what? Many patients are misdiagnosed as Conversion disorder/ FND. It is quite rare and patients will have a high Thyroid antibody count even if they don't have thyroid disease. Apparently, the antibodies attack the brain. Treatment is with steroids and seems quite good in most cases.
You may already know this information so forgive me if you do. It is just what I have found whilst researching after being diagnosed with FND ( which I don't think I have! ) I had to put the info out there in case it helps anyone.
If you need more info just ask.