If your character has a chronic illness or chronic pain please understand that they have already made peace with a version of their life that other people would find unbearable. They are not constantly in crisis. They have adapted. They have systems. They know their body in a way healthy people never have to. They are also exhausted in a way that doesn't show and angry sometimes in a way they feel they're not allowed to be. Write that competence and that exhaustion together. Both are true at the same time.
To add onto this, as someone with a chronic pain condition, there will also be moments when your character is just done. When they're so desperately tired of hurting they feel like they can't do it anymore. Because they want to be able to things able bodied people do with such ease and that's just not an option for them.
