Despite all expectations, Marty actually pretty much like this moment. When the danger is gone, the pain is still noticable, but bearable, at least until he will need to get up. So he’s just lying there watching his blood slowly flowing down over his body. There was times, when this view was scary, he still remember the first time this happened. He was really sure this is death, he was crying until he fell asleep, but then he wakes up next day and everything…well, not everything was ok, he was tired, hungry and barely able to walk, but he was alive and relatively safe, that was like a miracle that day (Although the wounds weren’t bad enough to could kill him. You know, fear makes everything look worse than it really is). Since then watching his wounds bleeding, while being in some safe place, is somehow calming for him. It’s a symbol, symbol, that worst things are over, symbol of brighter future, symbol of hope.
 
But don’t understand it wrong, despite this moment is strangely comfortable, the wounds themselves are still at least annoying and Marty surely wouldn’t hurt himself intentionally just for this. Although how often he gets into dangerous situations, is suspicious.
 
I should also clarify, that Marty has high regenerative ability, means his body always return to the original state. Could take weeks, months at worst, but it always happen. That’s why he doesn’t have any scars, despite this happened many times. It also makes him immortal in terms of age, however he still could die from other reasons, like fatal injuries or poison (but that never gonna happen as long as I am the lord of his fate.)