It could be mild OCD. It takes various forms, but is usually about irrational thoughts and fears. I suffered with it severly as a child and while I could remember some things vividly, other things would go clean out of my head.

I think mercury might cause it because it's thought most to affect the mind and nervous system, and both cause OCD - it's the mind that suffers, but it's caused by interference in neural pathways in the brain due to low serotonin.