Hit Points are an easy way of keeping track of how much damage your character can take before he or she dies.
The narrative aspect should totally be up to the DM/GM/Ref/Judge, if a book tells me how to narrarate, I will not buy it or I will not listen. The DM/GM/Ref/Judge should be incontrol, not a book.
So how do I justify it?
Ever been in a fist fight?
Those normal blows that barely hurt, theyre like normal hits, those times you get the wind knocked out of you or knock you down or hurt you more, those are critical hits.
Technicallly you can only take so much before you start to fall apart, so in theory if a normal hit does 1d3 non-lethal (which in itself is sort of unrealistic, but we'll go along with that) you (being a 1st level character [even though we are more like 0-levels, sorry if that offends you, but the majority of us are]) only have anywhere from 1 hit point to 7 hit points.
So can we only take 1 to 7 punches?
Depends on who is throwing the punch, but I've seen big guys knocked clean out by a single fist, critical hits perhaps?
This is the point I'm making, I have never used a healing surge, I have been in fights, both 'for real' and some for fun. But I have also never needed a day of rest to repair nor have I ever had to go to a church and ask for healing (although forgivness for one, but we're not going there)
You could argue "But that is non-lethal!"
I broke my nose in a fight, by the end of the day I was feeling better, I just had to catch my breath, a 2nd wind makes sense, but the overall healing I needed was minmal. Even when I had a PVC pipe broken across my back I didn't need a cleric's healing, I just walked it off, it left a cool bruise, kinda awkward to sleep but overall I was okay in about ten minutes.
So the narrative aspect of the game is what makes sense, but mechanics are, however, flawed. But it works the best so why complain?
Healing surges are a good idea, but mechanically wrong. I never willed myself back together (well..once was with ice, but it wasn't just my mind that did it) so I find it fairly 'fantastic'. But D&D being a fantasy game, it works for me. I do think a 'random' health regeneration would work better, but thats just me.