By way of Darkest Dungeon, I drafted out an idea for Sanity rules for ICRPG.
Sanity (aka stress) is a “double scale”, from 0-100 and 101-200. The first segment is “temporary” and the second is “permanent”.
Every time you accumulate stress – even a single point – you roll d%. You want to roll over the new value if your stress scale (meaning, if you have a stress of 25, and you gain 10, you want to roll 35 or higher).
Success means you’re OK; nothing happens. Failure means you gain an affliction. Make a note at which score you gained the affliction; you might want to note it something like “(52) Hydrophobia”.
When your stress goes over 100, things change slight. You still roll to gain afflictions against d% (but on a 1-100 scale, eg stress of 125 equals a target of 25). You do not need to remember the score, though; you can note them something like “(permanent) fear of breakfast”.
Afflictions gained above 100 are permanent. Lowering your stress does not make them go away. At 100 or less, any afflictions are temporary and as soon as your stress level goes under the level at which an affliction was added, it goes away.
You may reduce stress by plain ol’ rest, prayer, carousing or other vices, or some other activity (noted on your character sheet). Rest removes d4 per week, more advanced methods d6. Advanced stress methods may also require coin; if visiting the brothel helps, you gotta pay. You cannot use ALL methods of stress relief; you must chose vice or virtue. Those choosing vice cannot pray to remove stress; those choosing virtue cannot engage in pleasures of the flesh to remove stress. Other methods (eg loot) exist to remove stress and restore sanity.
(You don’t have to pick virtue or vice ahead of time, but once you pick, you’re committed!)
As above, anything gained as permanent cannot be removed through regular methods. It requires loot, coin, or something special to remove afflictions gained as a result of permanent stress.
If your stress level hits 200, you die or go irrevocably insane; your choice.
TODO: List of afflictions.