As a professor one of my students had a seizure then stopped breathing, during one of my exams. There were fifty students closer to her than me, yet somehow I found myself giving aid, as everyone else either dialed 911 or swooned "there goes my professor!" There was that second where all these thoughts went through my mind, but then she started breathing.
As for false accusations, there's a principle that accusers should understand but don't: NEVER assume you're the craziest person in the room.
I was on a plane once where a man donned a helmet and knee pads and attempted to open the door to the outside. I'm know that is an impossibility in the air, but instinct says stop it. Several men charged the guy and held him down until the flight touched down but it was interesting to see the reactions from various people.