ME/CFS.
It imposes a strict stamina limit. If you go over the stamina limit your energy levels will be reduced, you'll get dizzy, feel ill, get headaches, etc. If you go over too much or too often, your stamina is permanently reduced and you start taking physical damage. You won't know if you've gone over the limit until a couple of days later.
Shitty design. Totally ruins gameplay.
It's the worst. Let's hope they patch it.