So sorry you're not feeling well, Anika -- and in several regards no less.
I think the goal you set (post #7) to simply do it as you can is a good one. Balanced. Agree that "must" would be too harsh, and set you up for a worse mental state. I totally relate to your trait of finding it very hard to hold back and not go at something full bore. Like being naturally wired to walk fast (and pretty far). It is so hard not to gravitate to it out of default! But I no longer can. It's not laziness. I desperately want to be able to still do it.

Though obviously not like lupus, my hip has recently taught me something (well, it's trying to anyway). Is is:
Slacking and not being able to are two very different things.

It's so hard to accept that what was physically no big deal before is a very big deal now. But what would it prove to push it too hard because of a stubborn and unrealistic "should" attitude only to land back in the ER? Still working on where the line is between effort that is positive and helpful and that which is over-reaching and harmful. And it seems you are looking for that line as well. Listen to your body, even if it is telling you things you are not used to hearing. And don't wait till it is shouting and screaming.

Taking time is NOT selfish! You NEED to take the time to properly care for yourself! In fact, let's call it "using" time, not "taking" it. And you want to use your time wisely and in a balanced way, right?

Hope you get to feeling better soon.

(I've been only erratically on here lately too. Don't worry about that - it happens!
Oh! Trying to gain a bit of weight here too -- that's a goal in itself. )