I'm not a great sleeper, even when I'm in my bed, it's dark and quiet, and I'm tired, so I've never worried about falling asleep at the wheel, but it happened one time. I was around 30 and between marriages. I had gone to a couple back-to-back parties and had been awake 30+ hours. Driving home on the freeway going 70, I got woken up by my tires going over the lane marker dots. I couldn't have been asleep for more than a moment but it scared the complete crap out of me. I drove home with the window down (it was cold out), the stereo up, and smelling like adrenaline. I've never pushed it like that again.