If you fall asleep while you're doing it, then my guess is you're doing it wrong. That said, how CAN you do it wrong??? It's not exactly rocket science. And I don't even want to try to imagine someone who's so boring that they even bore themselves.
I fell asleep one time with the glass phallis in me and the fresh battery in my mini vibrator run out of juice all the while a porn on my tv on a continuous loop.