In my case, def had to do with food quality at lunch putting me to sleep in afternoon! Also, perhaps chemical sensitivity. The school was brand-new, and had that new smell.
Where did you hear that mercury can also cause this? Would be new to me!
Good to see you here! BTW, if you want others to comment on this, would be good to start a new post. Otherwise, folks may miss your post. Some only check the last page or so when they use the site, have read the older posts b4!