At least at that hospital (and I’ve seen it at subsequent hospitals), there was a list that we would make so that anyone who really didn’t want to be at work that day could call up to 24 hours in advance and request the day off if we were overstaffed. We called it a “hospital convenience day” and the nurse would generally get to go home on the provision that if we suddenly got an influx of patients they needed to come in within 1 hour and finish their shift. I think they got paid 4 dollars an hour for the time they were on call. If we couldn’t find enough nurses to accept this, they we could just let them go for the day but they didn’t get paid.

Not sure about the gastroscopy, though.