other ideas about selenium

Selenomethionine deposits in tissues, like the brain, in higher concentrations than other selenium forms. Although it can counteract mercury, lead, and cadmium, making it less toxic, it will stay stored in the brain. I'm no chelation expert, but it makes more sense to remove heavy metals from the body that do not belong there.

If I were you, I'd stop supplementation and resume intermittently. Sometimes, all it takes is a break.