Microsleep is short bursts of sleep, often experienced without the person even being aware they took place. They can be experienced by anyone who is tired, but the individuals most at risk are those who work night shifts, have a sleep disorder like insomnia or sleep apnea, or are sleep deprived. You don’t always notice when it happens. It is a brief, unintended episode of loss of attention associated with events such as a blank stare, head snapping, and prolonged eye closure which may occur when a person is fatigued but trying to stay awake to perform a monotonous task like driving a car or watching a computer screen.
Microsleep is most likely to occur at certain times of the day when the body is programmed to sleep, such as pre-dawn hours and mid-afternoon hours. Microsleep periods become more prevalent with cumulative sleep debt. In other words, the more sleep deprived a person is, the greater the chance a microsleep episode will occur.
“When we are sleepy, we make mistakes, our attention wanders and our vigilance goes down,” explains Dr. Chiara Cirelli of the University of Wisconsin — and that’s because our brains are already partially asleep. When people go beyond sleepy, though, they can lose consciousness for a few seconds in a phenomenon known as “microsleep.” You don’t have the faintest clue you micro-slept at all.
A study published in the January 2014 issue of Human Brain Mapping, researchers had well-rested participants track a randomly moving target on a computer monitor with a joystick for just under an hour. The continuous attention this required led to a whole lot of microsleep: participants experienced 79 microsleep episodes, on average, lasting up to six seconds each. In studies like these, participants usually recall having been wide awake the entire time. That’s probably because, during microsleep, it’s not your whole brain that loses consciousness. It’s often just a single region or even a handful of neurons.
As you might expect, experiencing microsleep during any task comes with a dip in performance. That’s why it’s especially dangerous to drive or operate heavy machinery when sleep deprived — which people do more than you might guess.