In trouble for working too hard?? What?

Today my boss called me in for a "meeting", which meant I was in trouble. I quickly ran through all the things I've done wrong lately. It could be about being late every day. I really am about 7 minutes late every single day. Dropping Lucy off just adds time, and I'm not willing to drop her and run. I help her take off her shoes and make sure she's all settled before I go.
It could be about the parenting class I recently started teaching. It could be about wanting to know exactly how I'm spending my time...hmm...what else. Maybe they overheard me complain about something?
No. No, it was none of those things. It was that my boss had seen me doing a massive project that hadn't been assigned to me. The person it had been assigned to is, excuse me, out of her league on this one. And I could do it. It was giving me a headache and making me hate life, but I could do it faster than anyone else I could think of. And I didn't mind doing it.
I asked if she was worried about me not doing my work while working on this project and she said no, that I hadn't been shirking any of my duties.
She simply said she didn't think I was paid enough to take on that kind of stress load, and that the person she'd assigned it to should be the one doing it. Most bosses would be THRILLED to have an employee doing work for less money. Not mine. She said she's worried that I'm not concerned enough about my own health and my own happiness.
I tried to assure her that I feel fine, and I don't mind doing it. But she wasn't having any of it.
So, in short, I got in trouble for working too hard. Guess I'll try to spend more time on facebook at work.