It's not exactly sleepwalking, but during the Diablo 2 beta, a few of my friends stayed up for I believe at least 60 hours straight doing nothing but sitting in front of their computers and playing. After 48 kicked in and they were still staring at their screens, one of them tried mousing down to the physical degauss button on the monitor before realizing he had to actually lift his hand and press the button himself. After 60 hours or so, some of them were falling asleep, but one of them was seeing giant gnomes at the bottom of the stairway and was trying to ninja roll his way to the bathroom so they wouldn't spot him.

Another time, one of my buddies was explaining in depth a character build for Guild Wars he wanted to make while he was completely asleep. He was even throwing in skills that would be learned and how they could be used against certain things, some of which he made up off the top of his unconscious head.

This was all the same guy. He's an...interesting character.