Douglas Harper's Etymology Dictionary
1912, probably a back-formation from decompensation. Related: Decompensated; decompensating.\n\n\n
Wiktionary
vb. (context medicine psychology of a bodily organ or mental state English) To deteriorate in function due to an inability to invoke normal defensive mechanisms that compensate for ailments and other stresses.
Usage examples of "decompensate".
I went on, 'The more he decompensates, the greater the likelihood he'll make a mistake and we'll get him.
I know some authorities believe sociopaths are really thinly veiled psychotics - Cleckley wrote that they wore a mask of sanity - but they don't usually decompensate and turn psychotic, do they?
When Ted Bundy decompensated, his crimes had escalated from spree killings to the orgy of the crazed multiple butcheries he committed in a Florida sorority house.