Perhaps you remember the Mad Hatter in Alice in Wonderland with a poor memory, insomnia and excitability. Mercury is used in the manufacture of skin medicine, dental amalgam, plastics, cathartics, paints, fungicides, cosmetics, and scientific instruments. Fortunately, its use in dental amalgam has proved safe with very rare exceptions. Mercury used to be used in the treatment of syphilis and in diuretics, but modern safer treatments have replaced medicinal uses. Mercury is still found in some folk medicine prescriptions and should be avoided.
Heavy metals are, in general, foreign to the body.
They are excreted in the tears, saliva, sweat, bowel fluids, and urine. When in excess, they get deposited in the brain and peripheral nerves, the liver, the bone marrow, or the kidney and rarely in the heart muscle. They don't all do all of these things, but knowing these possibilities give a framework on which to build and store knowledge of this area of medicine. If the metal is inhaled, there may be a toxic pneumonia. Some metals also interfere with certain enzymatic processes.