I'm really not seeing the need for narrative retconning or pure-metagame mechanics here. All that's needed is a recognition that 4E hit points are more a mental/spiritual state than a physical one.
Here's my explanation:
#1: Hit points represent vigor and fighting spirit.
#2: When you get hit, you suffer injuries which sap your fighting spirit. The physical extent of those injuries varies (see below).
#3: A hit which puts you into Bloodied is a superficial gash, flesh wound, stunning blow to the head, et cetera. A hit which puts you into negative hit points is a severe and potentially mortal injury. A hit which puts you down to (negative one-half maximum) hit points is an insta-kill; you were decapitated, stabbed in the heart, et cetera. All other hits are minor cuts and bruises.
#4: Recovery of hit points equals recovery of fighting spirit, not necessarily healing of wounds. Being the bad-ass hero that you are, as long as your spirit is strong, you can fight without substantial penalty even when you've been stabbed in the belly. You'll be staggering and soaked in blood and in a haze of pain and shock, but none of that will cause you actual mechanical penalties.
#5: As a qualifier to #3, if you are knocked down into negative hit points a second time, you may at the DM's discretion succumb to your existing critical wound rather than taking another one. (This prevents the situation where a character is walking around with six different not-quite-mortal wounds.)
So, if you've been taken negative and then used Second Wind and the like to bring yourself back up to full hit points, you've still got a severe wound, and it will be days or weeks before it heals. But your spirit is strong, your will to fight is undiminished. You can keep going despite your wound... unless you get taken down to negatives again.
There. Internally consistent system, no retconning, no metagame-only mechanics. It merely requires accepting that 4th Edition D&D is Cinematic with a capital C.