At first i used to tell people but i have learnt my lesson so i dont anymore, i just say i have thyroid probs and because this is recognised people do take you seriously.
I went to an interview at my local job centre, i said i couldnt take on a job cos i have thyroid probs and they were really sympathetic but if i had said it was because of mercury poisoning i know the look they would have given me, a blank stare, and thinking i was a nutter.