You probably didn't fall asleep, I'm guessing you blacked out. Memory loss was a problem for me at high doses like that. When I used to have a big bag of powder I would take it all the time so my trips weren't that great. I would attempt to recapture the euphoria of my early trips by increasing the dosage and often I would end up with blacking out. Signs are lost time, "falling asleep" (how can you fall asleep? DXM keeps me awake, unless I pass out from taking to much), waking up in weird places