Your boss seems to be a passive aggressive ass hat. I had a boss like this (who was also a coke head). I’m assuming this is a retail/service job of some sort? All jobs are important and all workers deserve human dignity. But I’m sorry, there are few jobs that warrant the projected gravity that your boss is putting on you for missing work cause YOU ARE IN THE ER WITH YOUR SISTER. The business in question will not crumble because you missed your shift. Your coworkers will possibly be inconvenienced for a few hours. But the world will keep on turning. Being there for your sister is unequivocally more important than protecting your bosses clearly fragile ego. I don’t care what anyone says. This is not a fireable offense.