(My sister kept coming out with lines like, 'see, you can do more than you think', and 'use it or lose it', but she's only seeing the outside, not what I'm actually feeling, or what it does to fatigue levels).

Grar! :(

I'm sorry :(

Just because someone CAN physically do something (that has adverse consequences), doesn't mean someone SHOULD physically do something, not unless they have access to unlimited free physiotherapy treatment...