The boredom of being on a closed track -- about 1/8 of a mile in length with two loops at each end -- exacerbated my fatigue. I could feel my eyelids drooping. My head started to slump. Soon, I found that I had been driving for brief stretches without any memory of it. Still, I pressed on.
About 20 minutes in, I suddenly awoke to find that I was off the track and driving on the grass next to it.
Shocked, I yanked the steering wheel and brought the vehicle back onto the road. I was scared and adrenaline was now pumping through me, bringing me to full wakefulness. It would not last long.
Soon, I was again feeling groggy and had increasing difficulty keeping the minivan in the middle of the paved road.
I was now going down a steep path toward unconsciousness but I struggled to continue. I was making the mistake many drivers make, convincing themselves they can go just a little further to their destination.
"We often delude ourselves into thinking that we decide whether or not we're going to go to sleep," Czeisler said. "'I'm just going to go another 10 miles. It's only half an hour to my house.' When you build up enough sleep pressure, you automatically make that transition to go to sleep. It can happen in the blink of an eye."
I drove an hour and then I just could not go on.
"In the words of [boxing great] Robert Duran, 'No mas,'" I said, pulling off the road and putting the transmission into park. "I'm done."
Back in the lab, Czeisler showed me just what had been going on in my brain while I'd been driving.
Pointing at the jagged lines on a chart propped on an easel, he said: "This is evidence that you're falling asleep."
He showed how my brain waves revealed the onset of sleep again and again. Then he ran a finger along the lines corresponding to my eyes blinking more and more slowly -- another tell-tale sign of the fatigue that had been washing over me.
I asked about the episode when I had run off the road.
"Yes," he said. "We could see it coming in your brain wave recoding."
He said I was asleep five or six seconds. But what truly shocked me was when he told me that I'd micro-slept a total of 22 times. I had only remembered dosing off twice.
I was lucky. I had been in a highly-controlled situation with safety precautions while driving just 15 to 30 miles an hour.
Every day, thousands of sleep-deprived Americans go whizzing along at speeds of up to 70 miles an hour. Many of them are aware they're exhausted but they are convinced -- as I was -- that they can outrace their own fatique.
Too often, it's a race they lose.
Yes, coffee and other forms of caffeine can stave off sleep, but only for a while. The only real solution: Pull over where it is safe and take a nap.