Are you a menace to society? If you didn’t get enough sleep last night but still got behind the wheel this morning, the answer is yes.

According to a recent study sponsored by the National Sleep Foundation (NSF), nearly two million people have had accidents or near misses due to driving while drowsy. More than half those polled said they’d driven while overly tired during the year and nearly 30 percent said they did so at least once a month.

Yikes!

It’s a misconception to assume you can stay awake by force of will, says NSF Chairman Thomas Balkin. And people rarely realize they’re falling asleep until they do.

Think about it. How many times have you nodded off, then suddenly jerked yourself to consciousness? During the time it takes you to whip up your head, you could drive over an embankment, through a median, into a lake, or headfirst into an oncoming car.

Forget the quick fix

Caffeinated beverages, blasts of cold air, loud music, and other “fixes” are no substitute for what the body craves: rest.

How do you know if you’re too tired to be behind the wheel? The NSF says to watch for these symptoms: difficulty focusing, heavy eyelids, persistent daydreams, repeated yawning, nodding, and realizing you’ve forgotten the last few miles driven—suddenly wondering “How did I get here?” or thinking “I don’t remember passing that landmark.”

If you’re suffering these symptoms and don’t have another driver to spell you, consider taking public transportation or finding a rest area or motel, then stopping for the night or at least a long nap. You may balk at the delay. But it’s better than being delayed permanently—and perhaps permanently delaying someone else as well.