Hi:
I also was diagnosed with Functional Disorder through Mayo. It’s what they do when they cannot find or do the proper tests. I finally was diagnosed with Autonomic Dysfunction through the Cleveland Clinic. I do no like the Mayo Clinic because this is the third time that they diagnosed me. I am so done with that place.

I have had that diagnosis made too. My personal opinion is it is used all to often when a neurologist gets frustrated because all blood tests, nerve conduction studies, etc. are normal.
When they can't figure it out then you are labeled with FND or FMD. FND describes a problem with the brain receiving and signaling parts of the body. FMD is functional unknow movement disorder. In other words your diagnosis means little because they are totally unsure what is causing your symptoms. My experience with doctors who practice neurology is that there is a tremendous amount of unknown but the patient needs a diagnosis for insurance purposes.