Check out Boyd Haley's youtube videos on the subject.
He says people with a Hg problem have lower levels of Hg in hair.
Reduced Levels of Mercury in First Baby Haircuts of Autistic Children Amy Holmes, Boyd E. Haley, etc. http://www.safeminds.org/research/FirstBabyhaircuts.pdf
The highly autistic children typically showed very low mercury in the hair. In contrast, healthy children showed levels of mercury in hair that were consistent with the mother's level of exposure to mercury.
Similar for Alzheimers. I have link to paper if needed.
If you get the Hg fillings out consider an IAOMT dentist.