That was one possibility, and may actually be better than how I did it. I have a role of Doctor, and then I have Insane Doctor. Abilities and potentially Win Conditions are different between the two.Fun!
I take it when you become insane, you get a random insanity role (so that you can't game future games with knowledge of a specific role-insanity-feature)?
I was kinda trying to make it so that the insane role sort of followed on from the sane role, but that does impact the replayability of it. The problem I had is that using a generic insane role e.g. megalomania, schizophrenia etc. could potentially offend people who suffer from or work with that mental illness. Any attempt to characterise one of these conditions in a role would invariably be a crude caricature of a complex condition. I'm personally uncomfortable with doing that - mental illness is poorly understood as it is, and I'd rather not add to some of the sweeping generalisations.