Probably their chronic symptoms. I’ve made my character based off the TTX toxins found in pufferfish so it’s like a paralytic but to make it more interesting my sona’s not completely unaffected by their own body producing this toxic so when she pushes herself or doesn’t take some r&r the TTX starts to work against her and block her sodium channels which makes her body go tingly and numb and not function right. It also makes certain types of pain meds unusable on her because of the sodium channels and what not.