It is said that no one comes out of Azkaban with their sanity intact; not after facing the dementors for days on end. The most frequently used statement to back this up is spoken somewhere along that lines of, "After all, just look at that Bellatrix Lestrange- she went insane."
But to go mad, one would have to have been sane at some point, and the problem was that Bellatrix never was sane to being with.
All belongs to JK Rowling.
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