[lionhearted]

Super interesting question.

Quick take — it 100% can't be linear.

Take as an analogue a strain injury — https://en.wikipedia.org/wiki/Strain_(injury) — a first degree strain can heal quickly with minimal invasiveness; a third degree strain might never fully heal even with surgery and rehabilitation.

Some of stress is happening on a biochemical level — if your hormones get sufficiently out of balance, and especially if it leads to a downward spiral of short-term behaviors (alcohol, junk food, etc) then you might wind up in a seriously diseased state that takes a serious regimen to recover from. On the other hand, if you never get above some threshold of unhealthy biochemistry and avoid downward spirals of behavior, recovery should be expected to be quicker.

There's so so many variables that it's heavily confounded and hard to math out, but the relationship for sure has to be non-linear.