One day in February, I walked out of my class.
It was just out into the hall, so they weren’t really unattended. But I needed to go into the hall and breathe.
I can’t remember a time when my efforts felt quite so futile. I was giving reminders about what needs to go into the introduction of an essay, and every single seventh grader in the room was looking at an iPad or the ceiling or the sky out the window — not me. Not taking notes, not reading the board on which I was writing, not thinking about their assignments. Just totally spaced out and off in another world.
So I stopped mid-sentence, “You know what? I’m done. Not one of you is paying attention, so I’m not going to bother.”
And I walked out.
I took a few deep breaths, tried to go to some happy place in my mind, and then I returned to my classroom.
I didn’t bother continuing the lecture. I just let them work (or pretend to work, as several in that class do on a regular basis) and helped them individually.
That was a rough day.
Good Morning, Class! 
😦
Those days happen. Good move on your part. Better to breathe than to cry. My students were remembering the other day some times when teachers cried and what had brought them to that. Interesting to hear them talk.