You may not want to hear this but it is a good chance that you lost some focus. High School and even college pitchers tend to do this even in the middle of an inning. Strike out the first two guys then go 3-0 to the next hitter or two quick outs and go 3-0 to the next hitter. Sometimes when pitchers are dominating they tend to back of so to speak and just throw. This is why you will see a pitcher put it in cruise control then give up a hit to the 8 and 9 batters.
It could have definitely been mechanics but considering you strike out the side I'm not really sure how much your mechanics could have changed. It is very possible but probably unlikely, it sounds to me likeyou lost some focus.