Fable 3 - Well I didn't buy it, but my girlfriend did for birthday/christmas. We fired it up and after a while, my tiredness got the better of me.. I fell asleep multiple times. She wasn't too happy about this I don't think. It happened another time she came round, and another time when I tried to play it alone. Played it again with her last week after not playing it for a long time, and this time we both fell asleep.
I don't know what it is, can't help it. I sometimes can't stay awake when grinding for long periods on korean MMOs, and I've fallen asleep in some raids in WoW.. but this is weird.