Its happened a handful of times and ended in sex a few times
Once was with a really good female friend, late teens ended up falling asleep together watching a movie, woke up the next morning to her rubbing my morning wood, she was an absolute nympho said it was like that when she woke up suggested we do something about it, so we did.
Another was a woman i was trying to sleep with but she was all over the place playing lot of games and shit, she came on a camping trip with some friends and due to some issues with her tent we shared mine but she was still playing hard to get. We got drunk and passed out, instead of being in separate bags as planned in our drunken state we just put them together. Woke up in the morning spooning, i was rock hard and it was planted firmly against her ass, she said she'd been awake for a while and wasn't against morning sex seeing as i was already hard.
Last one was an old friend i'd reconnected with, she invited me to a Halloween party, she was newly single and several of her girl friends were suggesting she fuck me as a rebound, she wasn't having it though. I ended up crashing on her couch and she had the heat cranked so high in this place by morning i was down to my boxers, i woke up to her staring at me from a chair across the room i had a full blown erection standing proud through the front flap of my boxers, she said she hadn't planned on fucking me but she hadn't had sex in weeks and i had very nice cock so why not