It's slow acting, but close to 100% lethal, and you don't die nicely.
IMHO, that's just about the most horrible combination imaginable.
Despite aggressive chelation therapy, her condition rapidly deteriorated and three weeks after first symptoms appeared she fell into a coma described by one of her former students as not being "... the kind of coma I'd expected... She was thrashing about. Her husband saw tears rolling down her face. I asked if she was in pain. The doctors said it didn't appear that her brain could even register pain."
Wetterhahn died a few months later, less than a year after her initial exposure.