I've only had the privilege (lol) to be on perc once in my life so far. It was after a car accident (in 2000). I don't recall much from the month or so I was on perc w/bed rest. The GF at the time said I'd be out cold for 12hrs about 15mins after taking one. Yet I would have bet money on the fact that I was up for the whole day, lol.