I don't know if the question about madness from the screen writer
was directed to the group or to an individual, but here is my two cents.
When writing for a character who is "mad" or has a "psychotic incident"
I would suggest that rather than depend too heavily on source books
or psychological reports, explore your own potential for madness...
ask yourself the hard questions.... what separates your sanity from
some hypothetical other's insanity... what would push YOU over that line
which you have identified?  Human potential.