To quote an actual hero 'you never know until you've been tested.'
I honestly don't know what I would do, especially without knowing specifics. Is it people in danger and rescuing them would risk my safety but not necessarily end my life, like when those Thai boys were trapped in the cave and divers went down to save them? I guess it would depend on the danger - I couldn't go underground, in a cave, to do it ... but I might be able to edge out somewhere high and help people get back to safety. And do I have time to consider the options - or am I acting on instinct? are the emergency services on their way? Will I actually do more harm than good?
Or is it more like someone aiming a gun at someone and I get in the way? Again - massive chance that I will do more harm than good - I'm not trained to talk people down, so I probably shouldn't try it. And if they were pointing a gun at my mum ... of course I'd be willing to die for her but she wouldn't be willing for me to die for her. I know she would much prefer to die instead of me, so me being a hero to save her would actually be a selfish act in which I got to die feeling all proud of myself, and she lived the rest of her life with the misery, guilt and loss ... not very heroic, when you put it like that, is it?
As a teacher, I would be expected to shield my pupils from a mad man with a gun and follow emergency protocols to keep everyone safe. I would - because it was my job - but I wouldn't necessarily save lives, because I'm a teacher and he's a mad gun man - what can I do? All I can do is die first, which is not the same as sacrificing yourself for the good of others. I certainly wouldn't tackle a mad gun man - that's not heroism, that's idiocy.
There is an actual mental illness linked to the desire to be a hero - they engineer emergency situations (like burning down buildings on purpose) so they can run in and save everyone. Have a go heroes are not always a good thing, and it is a problem in our society that we have glorified the every man turned action hero in films so much that people actually think that in any emergency situation they can be the person to do the rescuing, that this is some kind of expectation on them, and that simply waiting and letting the experts come in and handle it is the coward's way out.