Thank you for your very quick response. I will look into your emails and especially google scholar ... any information on this subject will be most helpful to me ... my neurologist has sent me and I have had numerous tests done with negative results ... so far, I seem to be the mystery patient ... some days are better than others and I can almost function normally, other days I have to stop and start .. it is the standing part that is the worst ... sitting has no lightheadedness at all .. once again, than you for listening ... a Toronto, Canada patient ...