Today I can’t get up: what is sleep inertia?


Surely the phrase “I can’t get up today” has crossed your mind at some point just when the alarm clock starts to go off, as the song by Mecano said , the mythical Spanish pop group from the 80s. But the alarm clock is one of those machines that we have inevitably become accustomed to obeying.

And yes, we get up, but for a while we are drowsy, disoriented and our cognitive performance, let’s say, is quite reduced. The physiologist Nathaniel Kleitman already said it in 1939 : one is not at his best when he just got up, regardless of what time it is.

This common phenomenon is known in the scientific literature as sleep inertia , and it has come to be considered a third process in sleep regulation.

The two processes that have traditionally been in charge of regulating when we will have a greater probability of sleeping are circadian and homeostatic. The first would be like a clock that marks the most appropriate time to start the break; and the second, a kind of hourglass (or the compound called adenosine ) that measures how many hours we have been awake.

For our sleep to appear without difficulty, both processes must engage in a sort of coordinated dance, in such a way that the most appropriate time to sleep also coincides with the moment when the adenosine accumulated during wakefulness is optimal.

Well, there are those who have considered sleep inertia as a third process in this regulation . It would act just after waking up in the morning, counteracting the low probability of sleep that would mark the homeostatic process and the high probability of wakefulness that the circadian process would indicate.

What happens in that half hour after we wake up

Although the process of waking up has been studied less than that of falling asleep, the truth is that some data on neural activity show that the brain remains in a state more similar to sleep when we have just opened our eyes than before we began to sleep. sleep . In addition, it is also known that cerebral blood flow is slower in the transition from sleep to wakefulness than it was just before we entered the arms of Morpheus.

So there seems to be a physiological basis for our having a hard time getting going every morning. And evolutionarily, would it have any advantage? We might think that, in nature, if something wakes us up, it would probably be better to be up and running in a matter of split seconds. However, given the complexity of the neural mechanisms involved in the transition between sleep and wakefulness, one hypothesis is that sleep inertia would be a way of protecting this process by avoiding abrupt transitions .

On the other hand, this inertia means that when we wake up at night, it is usually easy to go back to sleep . Another hypothesis about the usefulness of gradual awakening would be to avoid dream intrusions into wakefulness , in the form of hallucinations, in case of waking up in the middle of REM sleep.

Although it is considered normal, there are factors that can contribute to increasing this trance. For example, not getting enough sleep at night and waking up earlier than our body needs will increase sleep inertia. The same happens if we drag a chronic sleep deficit .

The time of day or night in which the awakening occurs also influences: sleep inertia is greater when we wake up during our biological night , when the organism understands that it is still time to be sleeping. And does the phase of sleep in which we find ourselves influence? In this case there is some controversy: it is not clear if the inertia is greater when awakening in deeper phases or not.

How does sleep inertia affect us and how can we reduce it?

That failure to boot has an impact on different aspects of cognitive performance, but at what levels? On the one hand, there are studies that have only found effects on reaction speed . Others also indicate that the precision would be diminished .

In any case, the execution of complex tasks that require greater attention would be the most affected by sleep inertia. For this reason, it would be advisable to carry out activities that require memory, calculation, decision-making or psychomotor coordination after those first 30 minutes of wakefulness.

As shown, a retrospective analysis of more than 400 US Air Force accidents revealed that accidents associated with human error were most frequent in the first hour after awakening. As the reader surely intuits, sleep inertia can pose a problem in the performance of emergency service workers such as medical personnel or firefighters .

Although sometimes it is unavoidable, there are things we can do to make it less difficult for us to wake up. On the one hand, we know that little sleep makes inertia greater. We also know that if we wake up during our biological night, it will also take longer to start. Therefore, getting enough sleep every night and doing it at the right times can reduce this inertia. And if what we want is to reduce the inertia of the nap, the shorter it is (always less than 30 minutes), the less it will cost us to recover our performance.

In the case of on-call staff, although bright light upon awakening would increase subjective alertness, no beneficial effect on objectively assessed performance has been found. It seems that sound and music could be effective in reducing sleep inertia.

Based on what we know about thermoregulation and sleep, cooling the extremities could also wake us up, although this has not been proven at this time. And while physical exercise upon waking does seem to increase alertness, it hasn’t been shown to improve performance afterwards either. Caffeine could work if we take it before a nap , but it is not recommended.

In short: to reduce the consequences of sleep inertia on a day-to-day basis, try to get enough sleep each night. And if they have to carry out a complex and important task, it should not be the first thing they do after the alarm goes off.

Author Bio: Maria Angeles Bonmati Carrion is CIBERFES postdoctoral researcher and associate professor at UMU University of Murcia