Microsleep: How Your Brain Can Fall Asleep for Seconds Without You Noticing

ABC News' Dan Childs experienced microsleeps while staying up for 50 hours.

— -- If you're exhausted and in the need to zone out, you might actually be grabbing bits of down time called "microsleep."

The phenomenon can occur most readily when a person is sleep-deprived, when their brain is primed to switch into sleep mode at any second. While a person can appear awake and even have their eyes open, their brain may have slipped into sleep mode, maybe reaching the first or second level of sleep.

Dr. Ilene Rosen, a sleep expert and associate professor of clinical medicine at the University of Pennsylvania, explained if a person appears "zoned out" they might actually be catching some Z's.

"They might have been thinking about nothing," Rosen explained. "Something brings them back to focus attention."

During that period, Dr. Steven Feinsilver at Mount Sinai Hospital in New York, found evidence that Childs' was slipping in an out of consciousness after just a few minutes of sitting quietly. That becomes evident when a person is hooked up to an EEG scan to look at their brainwaves.

Certain brain waves called theta waves showed how quickly a person could be "asleep," Feinsilver said.