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Sleep inertia is a physiological condition which limits your cognitive and motor abilities after awakening. Almost anybody can experience this condition after waking up. It happens when your mind transitions between sleeping and wakefulness, usually when you enter deep sleep and wake up before completing the sleep cycle. You experience disorientation, drowsiness, and reduced motor dexterity, and it can take either a couple of minutes or even hours after waking up for you to recover from it. In most cases, you don’t have to worry about this because it is a normal part of life and it disappears after a while.

Symptoms and Causes

As we previously mentioned, the main symptoms are the feeling of grogginess, reduced cognitive and motor performance and difficulty executing tasks. Grogginess is a disoriented state where your mental activity and senses are dampened. Impaired motor dexterity and a decrease in cognitive ability is what increases the reaction time for any task or movement and causes low attentiveness. Apart from that, you can get deficits in spatial memory, heightened subjective fatigue and an increased desire to go back to sleep. Although we all have groggy mornings, every person wakes up differently. Individuals that are morning people rarely experience grogginess, while some have grogginess every day.

The symptoms usually occur after waking up, and this is the time when they have the greatest intensity. How long they last depends on multiple factors, and the time ranges from a minute to a couple of hours. The duration of sleep can have a significant influence on the severity of your sleep inertia. The most significant factor is the stage you are in before you wake up. Abrupt awakening during deep sleep generates more sleep inertia than awakening in the light sleep stage.

The cause of sleep inertia is known – it is the sudden awakening that occurs during your deep sleep or slow-wave sleep. It can also take effect when you have insufficient sleep duration because sleep deprivation also makes it difficult to wake up. Sleep inertia is most likely to occur if your awakening is timed much earlier than usual, like when you have to go to the airport or catch an early train. Waking up from deep sleep still leaves your body with high levels of melatonin that makes you feel sleepy. The more you sleep, the higher the melatonin level is. However, this does not happen when you wake up during your light sleep or non-REM sleep. Waking up at this stage of sleep slows down the heart rate, brain activity, and blood pressure, and you can be awake and become alert a lot quicker. There are also theories that suggest that the source of sleep inertia can be the buildup of adenosine, a neurotransmitter in the brain during non-REM sleep.

This occurrence can appear or get worse if you have any other sleep disorder, like delayed sleep-wake phase disorder or even sleep apnea.

The deferred sleep-wake phase is a disorder that creates a postponed ability to go to sleep with insomnia during the night. People that suffer from this have an unusually delayed major sleep episode that is connected to the dark phase of the solar cycle. Because of that, starting to sleep and waking up at an adequate time is very difficult with severe and chronic sleep restriction and deprivation. These night owls have problems sleeping because they are not able to fall asleep until late at night and consequently, they cannot wake up in the morning and tend to oversleep. The condition typically starts in teenagers and can continue into adulthood, and because it induces sleep deprivation, it can also lead to many other symptoms like insomnia, idiopathic hypersomnia or sleep inertia. Toddler sleep inertia is also present, but children grow out if in most cases.

Sleep apnea is a condition in which you have a temporary loss of breath while sleeping. During the night you get complete or partial obstructions which are blocking your airways. It splits your sleep into fragments and interrupts your sleep quality, and it often creates episodes of choking, gasping, teeth grinding, snoring, frequent urination, pauses in breathing insomnia.

When is Sleep Inertia a Problem?

An individual that is sleep deprived or gets waked from deep sleep, experiences sleep inertia in a more severe and longer period. In these cases, your ability to do any task or even see a mistake somewhere is very limited during sleep inertia periods. Many drowsy driving car accidents happen in the morning because of sleep inertia. A driver with sleep inertia is very dangerous since he has impaired motor and cognitive functions which severely affect the ability to drive a car safely. A study from 2006 showed that severe morning grogginess is actually more alarming than staying up all night. While both situations are precarious, it is important to remedy the bad grogginess before going to.

Sleep Inertia Treatment

Because sleep inertia is a big problem for some people, especially those who have to work extended shifts, a lot of research has been put into developing methods to help overcome this condition. People that work as emergency responders, medical professionals, or in the military need to have excellent cognitive ability and motor functions in order to respond to a call and help people in dangerous or hazardous situations, which is why they have increased the demand for a remedy.

Caffeine and adrenaline

The most common treatment we use for sleep inertia is caffeine and adrenaline. The adrenaline and caffeine stimulate the central nervous system which causes an increase in alertness and with a boost to your blood pressure and heart rate it also improves your concentration. Caffeine and adrenaline block the adenosine receptors, limit the effects of the adenosine buildup, stimulates the brain, increase your focus and reduce fatigue.

Caffeine is good at improving alertness and performance if you are stressed and sleep deprived. As a countermeasure for sleep inertia, caffeine is an efficient cure  But the tolerance and consumption of caffeine are very individual, and it can vary in its efficiency to minimize the effects of sleep inertia. Even though these help you function during the day, they are only a temporary fix of the consequences, and not sleep inertia itself, so they should not be used as a long-term remedy. Many reports have shown adverse effects with vast amounts of caffeine. Negative effects like increased anxiety and impaired sleep are common problems that people experience from high caffeine consumption.

Light

An excellent way to fight this condition is by exposing yourself to natural daylight. The natural sunshine you get with sunrise is a significant factor that minimizes the effects of sleep inertia. The light at dawn suppresses melatonin, a hormone that is in charge of regulating your sleep-wake cycles. Brief exposure to bright light doesn’t help immediately with sleep inertia, but studies have shown it can help reduce symptoms approximately an hour after waking up. Exposure to white light doesn’t help. Only natural daylight has been proven to aid sleep inertia.

Sleep and naps

Another way to reduce the symptoms of sleep inertia is re-entering sleep for a short period. When a person is tired and sleep deprived, a short rest can help minimize the effects sleep inertia has on you. However, more extended rests may induce reduced mental and physical fatigue, and even produce sleep inertia. However, small power naps might help you avoid it. 

To avoid sleep inertia, you need to wake up during your light sleep, also known as the quiescent sleep and non-rapid eye movement sleep. It is crucial to avoid waking up during deep sleep or the slow-wave sleep that happens around 30 minutes after falling asleep. If you’re taking a nap, you need to limit it to under 30 minutes, just before going into slow-wave sleep.

Sound and temperature

Sound and temperature are stimuli that are proven to be effective in helping with sleep inertia. The presence of mild sounds and a slight decrease in temperature of the extremities can minimize the symptoms and possibly reverse them. Sounds with lower frequency components than white noise can aid with sleep because they provide a constant, and auditory background which minimizes the impact of random noises on sleep initiation and promotes attentiveness in sleep deprivation conditions. A drop in temperature of the extremities can stop heat loss and promote the return of core body temperature to normal daytime levels.

Tips

 Optimizing both sleep quantity and quality is essential. Adults need from seven to nine hours of sleep to feel well rested and functioning. Not getting enough sleep impacts the length and intensity of sleep inertia, and sleep deprivation can even prolong it to several hours. A good approach to deal with sleep inertia is to time your morning alarm to the end of a sleep cycle that lasts around 90 minutes. The best time to set your alarm is seven and a half or nine hours after falling asleep. In order to better predict your wake time, you can’t use a fixed-time alarm because it’s difficult to predict in which sleep stage you’ll be in  the same time each day. Instead, you need to set the alarm for each night manually. If your fixed alarm clock wakes you up from deep sleep, you will end up feeling groggy all day because part of your body is still sleeping.

Conclusion

If you wake up abruptly, sleep inertia can last up to several hours, increasing your chances of making mistakes during any routine action. Apart from that, sleep inertia has many unpleasant and somewhat dangerous effects. Some of these effects are extremely risky for pilots, drivers, or any other shift workers.

The main effects are low performance and response time on tasks, lower productivity in the first half of the day and loss of concentration. Experiencing these symptoms leads to a reduction in memory ability and drowsy driving. Drowsy driving has been the root of approximately 20 percent of accidents, with an estimated 1.2 million crashes a year. It is vital not to operate any machinery or drive any vehicle during an episode of sleep inertia. With the limited reaction time and concentration, you will not be able to conduct any action.

Sleep inertia can happen regardless of the duration of sleep. Even a short nap can cause disorientation that can last up to twenty minutes. This situation can be extremely detrimental if you have to perform immediately after a rest. Individuals that are sleep deprived and nap longer can have severe disorientation and impairment.

Additionally, large amounts of caffeine you put in your body to suppress sleep inertia can affect your heart. A loud alarm clock can produce high levels of adrenaline, which also affects your heart.

 

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