That's an embarrassing question to ask after a night of sex. That actually happened to me - and not even because of alcohol. It was just at a role-playing convention. Our characters fell in love and one thing led to another. But when waking up next to her, I realized: 'Damn! I know her character's name. But I never asked anything about her. Neither her IRL name nor anything personal. We just talked in character all evening and then fucked.' ... well, the morning was somewhat awkward. But then again - she had never asked my name either. Still, I was too embarrassed to ask her that morning.
Luckily, we met again half a year later at another con and I got around to asking her name and she was relieved that I did. She had been as embarrassed as I. Then we had a laugh about the whole matter - and fucked some more. So all is well that ends well.