If you're sleep-deprived, you might experience what experts call "micro-sleeps," quick blackouts that prevent you from seeing things.
A new YouTube video provides an easy way to see if you're at risk. Watch the animated clip above and see if you notice certain things - like a building disappearing or a school bus changing color.
If you don't catch those changes, you're not catching enough Z's, Richard Wiseman, a U.K. professor who studies sleep, told ABCNews.com.
"Long-term sleep deprivation is associated with poor concentration, weight gain, heart problems, and an early death, so it's really important that people get enough sleep," said Wiseman, author of "Night School: Wake Up To The Power Of Sleep."
He also asks viewers about caffeine and alarm clock habits to gauge sleep-deprivation.
The video is part of Wiseman's "In 59 seconds" YouTube series.