Medically there are two separate phenomena here. You may have "passed out" -- which is a loss of consciousness. At some point you recovered from being passed

Medically there are two separate phenomena here. You may have "passed out" -- which is a loss of consciousness. At some point you recovered from being passed out (if you were-- we can't trust your memory), but you still had enough alcohol in your body to be "blacked out" which is the inability to form memories. People can be surprisingly lucid during a blackout. You also could have gone home mostly sober and drank enough you can't remember the evening.