The state one falls into after the sleeping pills take effect, but before one is actually asleep. A person experiencing ambienesia will often seem a little loopy, and will do and say things they wouldn't do under normal circumstances. The person will have no memory of the events.
Dude, I totes said I love doing yard work in that essay I wrote last night. I think I have Ambienesia!
The term used for amnesia after a night of Ambien or other sleeping/anxiety pills.
Bruce realized he was suffering from Ambienesia when he woke up this afternoon with "Marco" shaved into his chest hair and lipstick on his calves.