Yes. I understand.
I deal with chronic pain too.
I have such fatigue from showering. It's horrible. Sometimes I just rinse off quickly.
I'm out of breath and scared by the time I make it back to bed.
I have a routine that I do. It's a meditation technique.
It does get either harder or easier.
One thing about bipolar. You can count on change.
I hope you can find some peace.
Maybe an occasional bath instead of shower.