I guess I have a different definition of self defense. Based on your story, I think you both were in the wrong. He was wrong for hitting you. You weren't wrong for hitting him back. But you were wrong for beating him bloody. The self defense part of the fight probably ended early and you switched over to just serving an ass beating.
On a personal level I don't have a problem with what you did, but it probably wasn't legal. In court you might get off but there's also a good chance you'd serve time if you really hurt him and he pressed charges. It can be such a fine line that you take that risk any time you throw down. You also run the risk of the other person having a gun and being scary enough to use it.
IN STREET COMBAT THERE'S A VERY FINE LINE...IT ISN'T LIKE SPORT WHERE THE FINAL BELL RINGS...AND EVERYBODY STOPS
I HAVE WHOOPED GUYS ASSES BAD...AND THEY STILL HAD THE BALLS...BEATEN AND BATTERED, TO STILL ATTACK...
OR LEAVE AND COME BACK WITH WEAPONS...
JUST CAUSE YOU GET THE BETTER OF SOMEBODY...
DONT MEAN YOUR SAFE...SOMETIMES YOU HAVE TO REALLY HURT SOMEBODY TO THE POINT OF INCAPACITATING THEM
ALCOHOL,DRUGS,AND/OR ANGER CAN PUSH THINGS TO THE EXTREME.
IT AINT ALWAYS AS EASY AS IT SOUNDS.