What disorders can come from being the last survivor of a group?

Had felt a change gradually after a buddy killed my team. I feel pretty numb and generally lost but still happy with my life. I can't remember how used to feel emotionally before my first deployment. Like when you remember laughing at a really funny joke, but you forget why it was funny.

I have a hard time being frightened by anything. I don't have nightmares.

On my second tour I met a kid who was in a gun team also and everyone else was killed when they stepped on a bomb, but him. He was done with fighting and he seemed calm about it. I remember that's how I felt at the time too. That's when the weirdness set in.

What is this thing? Can one get your their personality back?