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What Is Sleep Inertia?

Young Man Suffering From Headache Lying On Bed

Young Man Suffering From Headache Lying On Bed

Have you ever been startled awake by something? It could have been a loud noise, a nightmare, or your cat telling you it’s time to fill the food dish – the results are the same. Sleep inertia kicks in when there is a sudden awakening that actually impairs the level of consciousness that is being experienced. Thoughts come slowly and there is a tangible interference in performing physical or mental tasks. This is happening because the body is still partially asleep.

For most people, sleep inertia will typically last between 15-30 minutes in the morning. It is usually experienced by those who rely on an alarm clock to wake up. In some cases, the grogginess that occurs with sleep inertia may last for up to 4 hours. Sleep inertia occurs in 9 out of 10 mornings where someone wakes up to an alarm clock.

So what can be done about this issue? The human body doesn’t like it if you only give it half of a sleep cycle. It wants to finish the process. For this reason, it will rebel against your efforts to solve this issue unless you attempt to solve it with additional sleep.

What Causes Sleep Inertia? 

The actual cause of sleep inertia is not known to medical science. It can happen during REM sleep or non-REM sleep. Some theories involving melatonin levels or vascular constriction have been proposed, but no real facts have been exposed despite clinical studies that have attempted to find answers. For now, we can simply recognize the risk factors and symptoms of sleep inertia and create responses based on what is being observed.

Why Is Recognizing Sleep Inertia Important? 

It can be very difficult to complete any task while suffering from the grogginess of sleep inertia. Our decisions are far from optimal and sometimes they might not even be rational. We are more rational prior to our regular time for sleep and experience our worst cognition in the time just before we wake up from sleep.

Ever wonder why you hit the snooze button even though you need to be at work in 15 minutes? It’s the sleep inertia telling you what to do. It’s probably better to come up with a good excuse than try to force yourself awake, however, because when there are mismatches between social sleep and biological sleep, the risks of obesity increase.

For every hour of difference that occurs, there is a 33% greater chance that an individual will develop obesity. Alcohol use, smoking cigarettes, and even caffeine use enhance these risk factors. Till Roenneberg and Marc Wittmann studied the effects of sleep inertia on workers who primarily worked overnight [third shift] hours. They found that the stress of sleep timing and inertia were so great that the entire population demographic had higher than average rates of diabetes, metabolic syndrome, cardiovascular disease, and cancer.

What Makes Sleep Inertia Worse? 

First identified officially in 1976, sleep inertia is the gradual process where the mind transitions from a sleep stage to a wakeful stage. Although we often perceive this as a fast process, it really is very gradual. This is because the mind prefers to make its way back through the sleep stages following a trail of breadcrumbs instead of getting there with a 100 meter sprint. 

There are four documented stages of sleep and each has a particular “wave” that is assigned to it. The average person progresses through these four stages every night, with rapid-eye movement (REM) sleep being an intermittent stage. When comparing Stages 1-4 and how they relate to sleep inertia, there is a clear link to a more intense incidence of sleep inertia in slow wave sleep at the fourth stage when compared to Levels 1 or 2.

The core body temperature of the individual also has a direct link to the intensity of a sleep inertia incident. When a sudden awakening occurs at Stage 4 of sleep when the core body temperature is at its lowest, the stage has been set for a very severe incident.

Why does this happen? Although the mind is shut down to active consciousness when we are asleep, it doesn’t cease to operate. Your heart keeps beating, the lungs keep moving air, and your mind can create dream states. When people are exposed to familiar odors when they are in the slow wave sleep cycles, for example, it can help the part of the brain that is responsible for memories to recall previous incidents where that exposure occurred.

This is also why audio cues can become part of a dream state. Have you ever hit the snooze button on your alarm clock only to have the radio or television become part of your dream? This isn’t lucid dreaming. This is your consciousness beginning to creep in for the day. It is also why the deepest stages of sleep cause the most intense forms of sleep inertia. The rapid change from one end of the spectrum to the other for the mind requires time for it to adjust to its new situation.

How Does an Alarm Clock Impact Sleep Inertia? 

People who regularly use alarm clocks to get up in the morning have an 89% chance of experiencing sleep inertia at some level in the morning. This is because time is relative to each individual. The world operates on a specific time, but the sleep cycle someone experiences is operating on its own time. Even with circadian rhythms in place, there is no real way to predict what stage of sleep anyone can be in when the alarm clock goes off at 6am.

Oversleeping because someone didn’t hear their alarm clock isn’t just a lame excuse to tell the boss. It is a very real possibility. If you use an alarm clock that is set to a fixed time, then there is a 55% chance that you won’t wake up to the sound of the alarm if you’re in a REM sleep cycle. There’s also a 51% chance that an alarm clock won’t wake you up from a non-REM sleep cycle.

This means you are more likely to sleep through the sounding alarm of a fixed wake-up time. These chances are also a reflection of the potential sleep inertia that is going to be experienced. Yet we continue to do this time and time again because there is that 9% chance that the alarm clock goes off at the optimum time during the sleep cycle so sleep inertia doesn’t happen at all. You hop out of bed and get your day started.

Does Caffeine Impact Sleep Inertia?

Although the effects of caffeine on sleep inertia have not been well studied, there have been some small scale studies completed. In one study, 28 adult volunteers were given a low dose of caffeine or given a placebo during an 88 period of extended wakefulness. Participants were allowed to have seven 2 hour naps during this time. Vigilance performance was tested after each nap immediately after an abrupt wakening.

The study discovered that caffeine was able to help people overcome the problems that sleep inertia may cause. This may explain why so many people have the urge to consume a cup of coffee or have an energy drink immediately after waking up.

The most interesting result of this study was the fact that the participants couldn’t answer for certain whether or not they’d been given caffeine. They simply began to process the information that was coming their way. Instead of dealing with caffeine withdrawal symptoms that may occur during the stages of sleep, this research suggests that what people are actually craving is a more reliable way to wake up and become immediately active.

What About Sleep Debt and Sleep Inertia? 

There is evidence that links the amount of sleep debt a person has accumulated to the chances of sleep inertia occurring at some point during the night or upon waking up in the morning. 85% of awakenings occurred out of non-REM sleep in the placebo condition during the caffeine study and it was more severe in coming out of a non-REM sleep cycle when compared to a REM sleep cycle.

Because of the feelings of grogginess, some individuals may attempt to counter their sleep debt by scheduling in a nap time. Even short naps, however, have been shown to lead to severe instances of sleep inertia. A nap that lasts for more than just 20 minutes creates the foundation for sleep inertia to occur. It can often take someone more time to orient themselves to the world after a nap then the actual amount of sleep that was received.

What To Avoid During Sleep Inertia 

Because of the grogginess that occurs with sleep inertia, it is important to put in some safety precautions. In the United States, the National Highway Traffic Safety Administration estimates that over 100,000 reported accidents to law enforcement are a direct result of driver fatigue every year. Those accidents cause over 71,000 injuries, more than 1,500 fatalities, and create over $12 billion in monetary losses every year.

Avoiding driving or using heavy machinery while suffering from sleep inertia is more than just a safety concern. More than 40% of adults in a National Sleep Foundation poll reported that they feel heightened levels of stress when they are driving while feeling drowsy. 32% of drivers who are drowsy admit to feeling impatient more often and 12% even admit to driving faster.

This same poll found that 1 in 5 drivers pull over to take a nap when they’re feeling drowsy. Because a short nap can cause severe sleep inertia, it is very possible for drivers to get back onto the road feeling worse than they did before their nap because of the changes in sleep stages to wakefulness.

Any important decisions that need to be made should be avoided during the stage of sleep inertia as well. This includes financial decisions, medical decisions, and certain decisions that may affect a person’s personal relationships.

How Can Sleep Inertia Be Treated?

Many people look to fix the symptoms of sleep inertia like they’d treat the common cold. Instead of looking at what is causing the problem, the symptoms of the problem are reduced instead. Caffeine and adrenaline are known to alter the state of mind during a sleep inertia incident, but they will not address the core cause of the problem.

Consuming caffeine on a regular basis can actually increase personal health risks in other ways. This is because caffeine boosts blood pressure and increases a person’s heart rate. The feelings of wakefulness are improved, but not without cost.

If sleep inertia is bothersome and constant, then the best solution is to remove the trigger which is causing the issue. For many, this means getting rid of the alarm clock. This might be difficult to do if you need to meet a deadline for getting to work, but it will eliminate the fixed time for waking up that can create sleep inertia. Taking over the counter sleeping aid medications to help you start sleeping earlier so that you can wake up naturally early enough to get ready and be on time for work without an alarm is another potential option.

Are You Ready To Stop Sleep Inertia? 

Sleep inertia is dependent on how long you stay asleep, how efficient your sleep happens to be, and the stage of sleep you’re at when you wake up. Although it seems like getting 9 hours of sleep should reduce the risks of sleep inertia, what matters more is the actual nature of the sleep that is received. If someone gets 9 hours of sleep that is interrupted every 45 minutes because of sleep apnea, the effectiveness of that sleep will not be the same as 9 hours of sleep with minimal waking.

Proactive solutions to treat sleep inertia will always be better from a long-term health standpoint than reactive treatments. A reactive treatment is useful, however, should sleep inertia occur.

Any sleep stage brings with it the chance to cause sleep inertia. Deeper stages of sleep create higher risks of more severe incidents. Plan your day accordingly, avoid the alarm clock if possible, and counter grogginess as necessary with caffeine to avoid the mental deficits that sleep inertia can create.

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