My friends never talk behind my back while I sleep because they know I can remember anything, any conversation while I sleep... They think I never even sleep at all haha...
It often happens that for example, I sleep on the couch, facing the wall for hours and out of nowhere, I talk... like when my friends were playing some video games with puzzles and they were lost, out of nowhere, I just tell them what to do, with my face stuck in the couch... It makes them go "WTF is he possessed?" but I'm conscious and somehow my brain still works at some few percentage and also sleeping at the same time. It's the same while I'm even in deep sleep at 3 in the morning or 8 in the morning etc... I always remember...
But when people ask me to do something when I'm sleeping, example "Do you know where the remote controller is?"... I never go "Arrrgh" and slowly wake up... I just BOOM stand up and run to go find the remote controller and give it to them and jump back to sleep without a word and they're like

"dude you scare the crap out of me!"
I remember everything... just that sometimes I don't understand why I was like that HAHAHAHA! I guess that's how "zombie brain" is...