I once worked as a Christmas help at the now-defunct Bradlee's (think upper class Walmart, lower class Kohl's). The final before Christmas, I did something, somewhere, that damaged my back - like constant back spasms. I could barely walk, and the pain when standing at the register was excruciating.
In tears, I went to the front-end manager and asked to be sent home. He refused. I went to the furniture area and borrowed a wooden stool, which I dragged behind the register with me so I could have a respite sometimes between customers.
When the manager became aware of my rebellion, he came and took the stool away. I was not allowed to sit during my shift. Period.
I asked him, "You do realize that was my only way to manage this pain, right?" and was told to suck it up and finish my shift - and don't even think about calling out tomorrow.
I had a line of about ten at that moment. I removed my apron, pulled the key out of the register, and handed them over. Grabbed my drawer to turn in. Said, "I quit!" And left him sputtering, "You can't DO this - I'll FIRE you! You'll never get another shift here!!!"
He'd entirely forgotten I was a holiday temp, and that it was Dec. 22. My last day was the 24th anyway... I never looked back, had my final check mailed to me.
Years later, when I owned my own shop, there was a comfortable draftsman's chair at the register for employees to use!
--Bored at the Bookstore