I was reading this thread in bed last night and kept disturbing DP with my snorts of suppressed laughter and sniffing because tears were running down my face! 
Quite a recent one for me which I've mentioned on MN before.
Went to a dear friend's 40th birthday party, very sophisticated affair, fully catered in their big house, marquee dance tent and uniformed staff, the works. I already feel out of place at occasions like that (I tend to get nervous, drink too fast and talk too much) but managed to not get totally hammered and didn't embarrass myself. Party went off well and the only people left at the end of the night are the host and hostess, two of their friends (a Spanish couple), the hostess' sister and cousin, and DP and me. All staying the night in four bedrooms. We all trundled up to bed at around 3am.
The next thing I remember is coming back from the loo and getting into bed and DP saying
"Where the hell have you been??". I told him I'd been to the loo of course, where on earth did he think I'd been? He said
"You've been gone for two hours!" I was telling him not to be ridiculous when I realised that my side of the bed was stone cold. I had absolutely no memory of anything after going to bed until peeing and getting back into bed. DP said that a couple of hours earlier he'd woken up as I went to the loo and lay there dozing, waiting for me to return so he could go too. I didn't return! After five minutes or so he came out to investigate and I'd completely vanished. He figured I must have gone into the wrong room, but short of opening each door in turn and hissing "Crabby!", he didn't see what he could do so he went back to bed.
We went back to sleep and when we woke up again there were gales of laughter coming from downstairs. I sent DP down to discover the damage, and he came back up laughing so much he could hardly speak (DP is not a man given to big displays of emotion, either 
) and refusing to tell me what I'd done. When I went downstairs they were all sitting in the kitchen and made me go round each one and give them a hug to see if it jogged my memory of who I'd cuddled up to during the night. I was absolutely 
The Spanish couple were sleeping in my friend's daughters' room, one in each single bed. In the middle of the night the woman woke up to find someone climbing into bed with her. She could tell it was a woman because of the longish hair, but it was pitch dark due to the blackout blinds and she couldn't tell who it was. After spooning her, I then rapidly started snoring loudly, splayed out in the bed and nicked all the duvet. Oh the shame. Rather than waking me up and firmly suggesting that I go back to my own bed, the poor woman took the spare blanket and slept on the floor! 
When she woke up again, I was gone - the phantom cuddler.
I'm profoundly grateful that it was her bed that I staggered into rather than her husband's - that would have been even more . I'm also grateful that she felt able to say in the morning
"Um... Something odd happened in the night..." rather than just saying nothing and assuming that this is what happens at English house parties - all smooth sophistication in the evening and then some drunken numpty gets into bed with you and steals your duvet!
Luckily everyone thought it was hilarious, especially how utterly mortified I was. I do have form for getting a bit disorientated in strange places if I've been drinking, like not being able to find my way out of the room to go to the loo when we stay at MIL's - DP has woken up on occasion to find me doing my Marcel Marceau impression along the wall saying plaintively
"DP I can't find the door!", but I'd never done anything like that before.