Derangement

GURPS Horror 142, page 147 mentions it as an option under "Gaining Corruption"
Unlike corruption, it isn't priced as a disadvantage (-1 cp per 10c: a 1cp:10c ratio). This can be speculated at though.
"Any cure capable of erasing -1 point of full-on mental disadvantages can remove -2 in Derangement" suggests a 1cp:2d ratio...
It is similar to corruption in that it is a potential disadvantage waiting to happen (points can convert) but one which can also fade away before permanently lowering point scores.
In both cases aside from the potential disadvantage, they also cause penalties to rolls.
Pricing stress as a startoff disadvantage would be even more controversial since it's shed so readily at a 1/10m rate similar to fatigue, and not a DAILY rate like corruption/derangement.
Corruption should probably be priced differently anyway since it's so easily shed and since it takes 25 corruption to cause -1 character point. It should be 25 corruption per value of disadvantage!
Based on the 1:2 idea of derangement, it should probably be tweaked further: either a 5c:1cp conversion ratio, or else it being worth -1 cp per 50 corruption. Will rolls only get ignored at 125+ so this allows for 2 levels.
Category:Rules