TL;DR looking for advice or encouragement. I'm having a hard time with standing up for my needs and not working myself to death despite being 16 years post tbi

The long story is I'm 26, tbi happened when I was 10. I've never been great at finding a good balance between working enough and not working myself to death. I found the sweet spot was around 15 hours a week and that worked great at the place I'm at rn until recently. Its a dog daycare/grooming salon and I finally have a chance to work the grooming room (I went to school for it and have groomed on my own for 5 years now). It's exactly what I've wanted for years but it came at a cost: my table opened up bc our fastest groomer quit with zero notice. Because we are a small two groomer shop, things are absolutely insane. My co-groomer is doing almost two peoples worth of work since I'm not fast enough yet to make up the difference.

It's only been a few weeks since I went from working 12-15 hours a week to 25 hours and it's already taking its toll. I am dead tired even the days I'm not working and I know a big crash is inevitable if I don't change.

I'm gonna request that I only work 3 day weeks and stop doing early mornings when I go in Monday. My boss and coworker are very understanding of my limitations and I know they'll accept it. Despite that I just feel so guilty putting more work on others. How do you all deal with that? I've never been good at standing up for what I need and tend to be a bit of a "yes man" and take the hit quietly.