The Real Reason It Feels Impossible To Wake Up To Your Alarm Clock

Many people know the unfortunate feeling of waking up and feeling exhausted. The alarm goes off and the immediate impulse is to hit snooze while barely alert and drift back into a beautiful sleep for nine more minutes. At first, it might seem confusing to wake up tired, especially after a full night's sleep. It would even seem like this might present an evolutionary disadvantage as waking up quickly would be important in evading predators. However, this is a known and studied phenomenon, often referred to as sleep inertia. Even though there is a title for this inconvenience, scientists are still working to understand the exact neurological cause, and what they have discovered so far is fascinating.

Researchers have found that the brain seems to come back online in functional stages. The speed of blood flow to the brain is lower after waking than before sleep for roughly half an hour, returning to normal waking levels first in lower-order brain regions, such as the brainstem and thalamus. It would appear that last to arrive at the party are the regions responsible for executive functions, like the prefrontal cortex. This is why being able to move around and take in sensory information is relatively easy, while thinking clearly might feel a lot harder.

Research also indicates that the type and amount of sleep prior to being woken up can have an impact on the level of sleep inertia one might feel. For instance, subjects who stayed up for longer durations of time tended to exhibit more difficulty becoming fully alert. So, pulling an all-nighter could have poor consequences for the following morning. Additionally, the racking up of sleep debt through multiple nights without sufficient sleep tends to worsen the effects of this phenomenon. 

Another factor is the time at which one is woken up. Cells in the body function on an internal clock, commonly known as a circadian rhythm. Since humans are diurnal (naturally awake during the day and asleep at night), circadian rhythms promote wakefulness in the daytime and sleepiness in the nighttime. Glucocorticoids, like cortisol, are key players in alertness and are often increased when it is time to wake up in the morning. Whereas melatonin, which helps sleep, increases at bedtime.

Scientists found that when subjects were awoken from a nap during the peak of the circadian rhythm, which is when the internal clock is set for high alert, their cognition suffered compared to subjects woken up during the most restful point of the circadian rhythm. Likewise, sleep inertia tends to be greater when woken up during deep sleep as opposed to lighter sleep.

Of course, the most important contribution to a better experience when waking up is getting enough sleep. Understandably, though, finding the ideal amount of time to sleep can be difficult for many. In these cases, science presents a few ways to avoid that heavy grogginess at the sound of your morning alarm. One interesting tip that might sound counterintuitive is to take shorter naps. Recall that some studies have shown that sleep inertia is exacerbated when woken from a deep sleep. Taking naps of 20 minutes or less can prevent falling into a deep slumber while still providing the benefits of some sleep.

For another interesting aid, one study showed that consuming some caffeine prior to sleep actually eased sleep inertia. This might seem counterintuitive since caffeine is meant to improve wakefulness. However, the researchers from this study suggest that this could be due to caffeine's role as an adenosine receptor antagonist. Adenosine builds up as energy is exerted throughout the waking period and is decreased during rest. Therefore, the authors postulate that caffeine helps reduce the effects of leftover adenosine stores from a poor night's sleep. So, while short naps and caffeine might not make up for lost sleep, these can be helpful in feeling a bit more rested.