So, something that occurred to me recently and I just tried testing it… It looks like the diminishing returns from resting can be reset by things other than just explicitly clicking on 'Rest'. For instance, in the Soothing Stacks encounter, if you choose to "Take a rest" that counts for the purposes of resetting the counter on using healing medicine. It's probably tied in to any encounter option where it talks about taking some time and you regain HP, though it might be worth categorizing such things.
Medicine / Discussion