Not a second thought to it....I'd do what I could. If s/he's in trouble, what harm can that person cause me - and how relieved and, well, frankly - out of danger - they would be. In the end, that's your objective. If you helped achieve it - excellent. We are the miracle creators. Whether you are religious or not - you can say that God acted THROUGH you, or you can say, as I believe, that basically decent human beings would jump in and help if, A.) they felt able, B.) they felt safe, C.) getting involved and making a mistake could make matters worse.
Hell yeah - I'd stop and help them - and stick around until transport/ambulance/resident director/social worker/group home manager/husband/wife/brother - whoever could be with, comfort, care for, and help him/her better than I. And if my help was truly no longer needed - then I'd be on my way - waving off whatever thank yous and (well, okay - I go for hugs - they are gifts of affection, warmth, and in this case, thanks - and they are precious) material attempt at gratitude offered replying, I believe karma begets itself. I'd want somebody to help me. And I have needed help many times in my life.
It feels good to be in the right place at the right time and, whether instantly or after a couple deep breaths, to do the right thing. :)