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Medically Reviewed by Dr. Sahil Chopra

Have you ever realized you just missed a red light turning green , or woke up due to your head suddenly jerking? You may have experienced what sleep scientists call a “microsleep.”

Microsleeps are 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.

Sleep deprivation and associated microsleeps increase on-the-job errors and car crashes. Multiple disasters have been attributed to microsleeps, such as the 1986 Chernobyl nuclear disaster and Challenger explosion, the 1989 Exxon Valdez oil spill, and multiple airline crashes.

What is microsleep?

Microsleeps are brief, unintended episodes 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.  These are potentially among the most dangerous consequences of insomnia.

Microsleep episodes last from a fraction of a second to two minutes, and often the person is not aware that a microsleep has occurred. In fact, microsleeps often occur when a person’s eyes are open. While in a microsleep, a person fails to respond to outside information. A person will not see a red signal light or notice that the road has taken a curve, which is why this phenomenon is of particular interest to people who study drowsy driving. Similarly, during a microsleep, a pilot might not be aware of flashing alarm lights in the cockpit.

When do microsleeps occur?

Microsleeps are 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.

Technically, everyone also experiences microsleep during sleep onset, as Dr. W. Christopher Winter, M.D. explains: “Sleep scientists define sleep onset as the first time you have 15 seconds of sleep within a 30-second period.…It’s not that the lights just cut off, the light flickers and flickers and then it’s off.”

What causes microsleep?

Microsleep can happen to anyone, but individuals most at risk are those who are sleep deprived or who have been performing a sedentary task for a sustained period of time, such as driving or repetitive work.

Individuals with sleep disorders that cause sleeplessness, such as insomnia or sleep apnea, are also at risk. In fact, microsleep episodes may help diagnose sleep disorders such as sleep apnea, which the individual may not be aware they have since it occurs while they are asleep.

  • Individuals with sleep apnea may get enough hours of sleep, but due to the apnea, experience poor quality sleep which can cause chronic sleep deprivation. According to the American Sleep Apnea Society, drivers with obstructive sleep apnea (OSA) are 2 to 4 times more likely to have a car accident. The graph below shows the link between sleep apnea and increased risk of drowsy driving, among adolescents.
Drowsy driving microsleep and sleep apnea

Source: CDC

  • Individuals with excessive daytime sleepiness, a well-recognized symptom of insomnia, often experience micro sleep episodes during periods of Excessive Daytime Sleepiness.
  • Microsleeps are one of the symptoms of narcolepsy, although they should not be confused with sleep attacks indicative of the disorder, which occur spontaneously, can last much longer than microsleep, and do not go away even when the person gets sufficient sleep.

What happens in the brain during microsleep?

While it is still not entirely clear what happens in the brain during microsleep, several studies have demonstrated that some parts of the brain appear to effectively fall asleep while others remain awake. This could account for selective loss of awareness without the person feeling he or she has been asleep.

A 2015 study published in NeuroImage kept volunteers awake for 22 hours and monitored their brain waves while they were placed in a dark fMRI machine. During microsleep episodes, the thalamus (the part of the brain responsible for regulating sleep) showed reduced activity while the parts of the brain responsible for sensory processing and attention (actions aligned with wakefulness) showed increased activity.

rats microsleep study

Source: ScienceDaily

In a 2011 study, rats were forced into a state of sleep deprivation by being kept awake for long periods of time. They began to show “local sleep” among groups of neurons affecting their motor cortex, despite EEG measurements of overall wakefulness in the brain and the rat’s physical appearance of being awake. This sleep deprivation affected the rats ability to perform complex motor tasks such as using a single paw to grab a sugar pallet, which may explain the simple mistakes humans make when they are sleep deprived, such as losing their keys or not realizing when a red light has turned green.

Part of the challenge in analyzing microsleep episodes is that researchers still have not developed an agreed-upon clinical diagnostic tool for microsleep. EEG recordings are often used in sleep research, but they are more effective when used at a macro-level determining states of sleep vs non-sleep. Changes in the brain caused by microsleep, on the other hand, are much more subtle, and characterized by sections of the brain falling asleep while others stay awake.

Drowsy driving and microsleep

According to the AAA Foundation, 16.5 percent of fatal crashes are a result of drowsy driving.  Sleep deprivation reduces a driver’s reaction time, alertness, and judgment similar to impairment from alcohol or drug use. In fact, studies have shown drunk driving can be as dangerous as drowsy driving.

More problematically, when people experience microsleep due to sleep deprivation, they continue to push through and drive instead of pulling over to sleep, according to a 2012 study by Queensland University.

Microsleeps are positively correlated with accident risk – the more instances and longer duration of microsleep episodes, the higher the risk of an accident. Researchers have used driving simulators to show that as individuals continue driving throughout the night, without sleep, the number of microsleep episodes, duration, and resulting crashes all increased.

What does this mean for night shift workers? Unfortunately, night shift workers are more likely to have a crash on the way home after a shift than when they’re fully rested. A 2015 study published in Proceedings of the National Academy of Sciences showed that during a test drive, 37.5 percent almost had a crash after working the night shift, compared with 0 who had full sleep the night before.

Warning signs of microsleep

Are you about to experience a microsleep episode? Consider the following warning signs:

  • You feel sleepy.
  • You have trouble keeping your eyes open.
  • Your eyelids droop or close, present a blank expression, or are constantly blinking.
  • You have difficulty focusing on where you are going or what you are doing.
  • You yawn a lot.
  • Your thoughts wander.
  • You feel moody or irritable.
  • If you’re driving, you drift off to the side of the road or have trouble keeping in your lane. You miss your exit.
  • Your head nods gently with a sudden jerk to wake you. The head jerk is often what makes people realize they experienced a microsleep episode, since the brain won’t recognize the short sleeps as sleep.

How to prevent microsleep

If you start to notice the warning signs of microsleep described above, try to get some sleep if you are in a situation to do so (pull over to a rest stop if you are driving, or stop operating heavy machinery if you’re at work).

At best, microsleep impacts your focus, causing you to miss your exit while driving, not hear a key piece of your teacher’s lecture during class, or be caught unawares during an important meeting at work. At worst, it can cause a car accident, or put your academic or career performance at risk.

Below are some tips for preventing microsleep on the road, in the classroom or at the workplace.

Preventing microsleep while driving

1. Avoid driving during times when you feel less alert.

This will include nighttime, when your circadian biological clock wants you to be asleep, or during the afternoon dip. This could also include early evening for morning larks or early morning for night owls.

2. Get sufficient sleep before a long road trip.

Don’t drive when you are sleepy, and pull over for a 20-minute power nap whenever you need a break. Turn the car off by taking the keys out of the ignition, as some states have laws against sleeping while a car is still in operating.

3. Drive with a travel companion.

A fellow passenger helps you stay awake and alert through conversation. They can also watch you for signs of sleep deprivation, and switch off driving responsibilities with you.

4. Keep your mind engaged.

Listen to upbeat music or an entertaining podcast or radio show to help your mind stay focused. There are many apps designed to help you sleep, and there are just as many anti-sleeping apps that will make a noise or vibrate to help you stay alert. Just be careful that you don’t become a distracted driver by looking at your phone.

Preventing microsleep during class or work

1. Stay alert by interacting with others.

Ask and answer questions in class. At work, engage in productive conversations with coworkers, or respond to your emails.

2. Keep your body moving if possible.

Fidget quietly by spinning a pencil or pen around. Stretch in your chair. Use a treadmill desk.

3. Take breaks.

Get up when you can to move around the classroom, or walk outside between classes to get some sun and fresh air. Take trips to the water cooler or take a walk around the office or parking lot.

General tips

1. Get enough sleep for your age.

For the average adult, that’s between 7 to 7.5 hours. For adolescents it’s longer, around 9 hours.

2. Watch what you eat and drink.

Eat healthy foods that energize you like complex carbohydrates and protein. Avoid alcohol if you are sleepy, as it makes one even sleepier.

3. Consider caffeine or vitamin supplements.

Caffeine can help you stay alert, but remember that it takes 30 minutes to kick in and lasts only a few hours. More importantly, it will not prevent microsleeps. Vitamin B and C supplements give you a boost of energy. Chewing gum keeps your mind and mouth moving.

Additional resources

  • Microsleeps are a symptom of sleep deprivation. Learn more about the causes of sleep deprivation and the dangers of accumulating sleep debt.
  • Insomnia and sleep apnea can cause chronic sleep deprivation that results in episodes of microsleep. Understand what causes different types of insomnia, and how to treat it.
  • Excessive Daytime Sleepiness is a symptom of most sleep disorders. Read more about causes, diagnosis, and treatment options.
  • If you believe your microsleeps may be a symptom of narcolepsy, discover additional symptoms and how to receive a diagnosis and get treatment. Share your experience and get advice from peers on the Narcolepsy Network Community and Narcolepsy subreddit online forums.
  • Tuck’s Drowsy Driving Guide offers an overview of the epidemic, as well as prevention tips and resources.


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