What does human reason become when it steps outside its limits?

There’s this chilling passage in Sebald’s Vertigo, a digression into Giacomo Casanova’s incarceration in the Doge’s Palace prison chambers

Casanova considered the limits of human reason. He established that, while it might be rare for a man to be driven insane, little was required to tip the balance. All that was needed was a little shift, and nothing would be as it formerly was. In these deliberations, Casanova likened a lucid mind to a glass, which does not break of its own accord. Yet how easily it is shattered. One wrong move is all it takes.

And, of course, now I want to read Casanova’s Memoirs. If you’ve read an edition that you’d recommend please let me know in comments. This new edition looks like the most interesting, though it might take a while for a version to appear in English translation.