I lived with a guy for about 2 yrs who did it occasionally. One particularly funny night - He woke me in the middle of the night -- never said a word - just kind of pushed my head down ... We had amazing oral sex - then as was his custom, he rolled over and went to sleep. Never said a word. I didnt think much of it and went back to sleep myself. Some time later it happened a second time, and I was more than willing. This time, halfway through, his eyes suddenly opened and he said WHAT ARE YOU DOING? I looked at him kind of like he was nuts. I asked "Don't you remember the first time?" He said ... Ummmm no. I said well too bad because that one was world class. He kind of laughed, we finished and went back to sleep. He had no recollection of the first time and no idea what woke him up for the second half of the second one. I never knew exactly what happened until a year or so ago when I learned about this. I often asked him if he remembered dreaming about sex during the night, but he never remembered. Yea, he was absolutely positively asleep for the first one. Another time, we were fighting and I was sleeping in a different room. In the middle of the night, he appeared in the doorway, took off his clothes and got in bed. In the morning, he looked at me and said "I came in here with YOU?" I laughed.
I have heard its kind of rare, but there are many men who actually do it. They react, move, respond and in the end climax, but they have no recollection of it. Shame huh?