Josephine, I used to feel the same way, but now I look at sight-reading practice much more positively. Once I got over how much lower my reading level is, I went all in and got lots of music at that level. I also struggle with chronic tendonitis, which limits my ability to play certain pieces or even how much I can work on technique some weeks. But my sightreading books are always there for me: they never stress my arms, even just 10 minutes of it feels like I'm doing something towards my learning, and several months later, I am noticing some progress. Finally, after the slower process of practicing a performance piece, there's something liberating about taking out easier sheet music and playing, and thinking, "Wow, I'm actually moving along measure to measure and (mostly) getting this!"