What is up with that?
I asked my boss if I could cancel my shift on Saturday morning, explaining I have problems with sharply changing the times I wake up on. It shouldn't be a problem as I am already doing the minimum of 3 shifts.
The boss didn't say she can't or not willing to. She told me that I will go to that shift. I told her I'll try, she said that there's no trying and I have to go to the shift.

Yes, maybe my request seemed childish. I didn't tell her anything about depression because I don't want to disclose those kind of details at work.
Calling me a "big kid" was belittling and I dislike her for that now.