could you elaborate on the "wizard with mercury poisoning archetype"? your post is the first i've heard of it that i recall
(With reference to this post here.)
The whole “physical frailty, irritability and social withdrawal occasionally punctuated by sudden manic episodes with delusions of grandeur” bit is largely derived from historical stereotypes about people with mercury poisoning. (In reality, mania and delusions are rare in mercury poisoning victims, but they got to be part of the stereotype anyway!) You tend to see this specific stereotypical personality associated with any profession that’s historically been prone to mercury exposure, ranging from hat-makers (as immortalised in the idiom “mad as a hatter”*) to lighthouse keepers.
I’m not sure whether there’s a specific reason that wizards – being a fictional profession – also tend to fall into that bucket, or whether they just picked it up by association; I want to say it has something to do with alchemists (who were notably prone to giving themselves mercury poisoning), but that’s speculation on my part – I don’t know enough about historical stereotypes about alchemists to back that up.
* to anticipate the inevitable well-actually, I’m aware that “mad as a hatter” probably originated as a corruption of an earlier idiom “mad as an adder”; however, its meaning drifted over time, and by the 19th Century it was firmly associated with mercury poisoning among hat-makers even if it didn’t start out that way.