A new study out Thursday has shocking results on the number of people who fall asleep behind the wheel.

One in 24 adults in the U.S. say they recently fell asleep while driving and researcher think that number is probably even higher. That's because some people don't realize it when they not off for a second or two on the road.

The Center for Disease Control and Prevention found that a little over 4% of U.S. adults said they fell asleep while driving at least once in the previous month. The study found drowsy driving was more common in men and in people ages 25 to 34.