My schnoodle bit me in my face

I've had my schnoodle for 3 years, he's the most loving dog ever but recently we had a mishap he bit me :( on my lip and I had to get stitches. I'm dumbfounded, lost, confused and not too sure where it came from. He's a mamas boy and follows me everywhere, my shock cones from the fact that he bit ME outta all people. Not sure if you can help dissect what happened, but I figured I'd share.