The MG Manual mentioned that a Myasthenia Gravis diagnosis "is frequently delayed months or even years. The unusual distribution and fluctuating symptoms often suggests psychiatric disease."
Myasthenia Gravis: A Manual for the Health Care Provider (PDF) - page 14
It seems to me that the false psychiatric diagnosis would fall most heavily on those who are insistent with their doctors that there is a problem. If you complain too much, and if you doctor cannot see the symptoms, then you must be crazy.
-Mark-