Yawn!
This is so simple to solve - you must be a moron if you can't see it. It's classic!
What we're seeing here is evidence of repressed somnambulistic trans-gender intrusive rectal activity and post-orgasmic guilt complex.
OK, so let's see if I can explain this in idiot terms......
OK - she goes to sleep, right? During the sleeping state her inhibitions disengage, allowing her true desire to be in possession of her own penis to take control. She sleep walks over to her knicker drawer and unconsciously attaches the strap on dildo to her nether regions, removing her pyjama top on the way back to bed.
Having driven the member northbound up your marmite motorway a few times, she suddenly wakes up, realises that she could be in danger of getting caught out and cleverly goes on the offensive, blaming you for taking advantage of her in her sleep, engaging in 'inappropriate sexual activity' with a sleeping and vulnerable female of impeccable morals. Evidenced by the now removed pyjama top.
You've been butt-fucked by a lady boy mate.
Hope this helps