France's King Charles VI, 1368-1422, believed he was made of glass, and had iron rods inserted in his clothes so he might fall over without shattering. Obviously he had to excuse himself from Kingly duties such as resisting England's King Henry V, as the Battle of Agincourt wasn't a safe place to be if you were made of glass, or French. Today, of course, he'd just be the beloved center of a moderately quirky room on a muck somewhere, maybe with a web ring.
It certainly seems like kings and queens were much more insane, on average, than the ordinary folk; but Europe had for a thousand years around four jillion little states each with their own royal family, and the quietly sane and competent royals, and the vast masses of people, leave less vivid legends behind. Until the invention of the celebrity in the 19th century you didn't hear about many other people. Still, I imagine any peasant living outside Rhiems in 1410 with the same madness didn't have anyone reinforcing his clothing and giving him space lest he shatter. He had to get on with life, chipped or not.
So assuming, as is fashionable these days, that most mental disorders have physical causes ... there's definitely a point where being able to act on them turns what had been personality into incapacity. In the alternate history where Michael Jackson's singing talents are never discovered, he sits up late nightly on FurryMuck or Altered Realities coaxing his transformation partner to turn him into an garage-kit statue of an anime guy again; I daresay that Jackson functions better in life than the one we have, where he has enough money and time to try it.
We all have little bouts of madness. There was one morning in ninth grade I woke up convinced I'd been replaced with an android, and it took much of the day to convince myself that was ludicrous on every front. (I had to do it by reason, which is intellectually unsatisfying; but I was too cowardly to see if I could bleed, and didn't know how to test whether it would be real blood -- and how to test it at enough points and times to be sure it wasn't a cleverly planted packet used to quell such fears without making myself look suicidal.) But over the course of the day and the interactions with everybody else I got over it, and it's now just a faint pleasant memory of something absurd I thought one day.
But if -- at that moment -- I'd told anyone, and they didn't laugh at me but went along with it, I could easily have turned what has to have been a late dream into a lingering delusion. Maybe mental disorders are something like certain cancers; people can be more or less prone to them for biological reasons, but it's only if one is triggered at the right time and by the right stimulus that it can grow and turn pathological? Obviously, I'm ignorant enough of biochemistry and psychology that I'm making what are probably either trivial or trivially wrong guesses, but I can't help wondering what insanities might be avoided, and what might be lurking and waiting for the right trigger.
Trivia: As late as the early 20th century British grammarians decried the word ``reliable'' as a new and barbaric Americanism. The word was first recorded in England in 1624. Source: A Short History of English Words, Bernard Groom.
Currently Reading: Tracking Apollo To The Moon, Hamish Lindsay.