I had that happen with DS1. He was sleeping in bed with me and I guess went for some milk in the middle of the night (not unusual for me to fall asleep with a boob out) and he I guess missed...
It has happened to me too! I never thought a baby could give you a hickey before. He gave me one and it hurt. DH saw it and was like, "Did A.J. give that to you?" I looked down and nodded.
Re: BFing mommies- nipple hickey from baby?