What if I killed an attacker in self-defense?

If, for example, I’m walking on my way home at night and a guy jumped on me and tried to hurt/kill me and I used self-defense but I killed him, what might happen?

What might happen if…

1) ...he hurt me (armed/unarmed) and I defended myself and I killed him?

2) ...he didn’t hurt me, he just tried to, and I defended myself and I killed him, what might happen to me?

3) ...I killed him and I never had the intention to kill a person, but I accidentally did because I’m defending myself?

And what do you suggest to do if something like this happened?