In order to measure the cognitive and motor deficiencies associated with sleep inertia, a battery of tests may be utilized including psychomotor vigilance task, descending subtraction task (DST), auditory reaction time task, and the finger tapping task. Causes
Studies have shown that abrupt awakening during stage 3 sleep, slow-wave sleep (SWS), produces more sleep inertia than awakening during sleep stages 1, 2 or REM sleep. Prior sleep deprivation increases the percentage of time spent in slow-wave sleep (SWS). Therefore, an individual who was previously sleep deprived will have a greater chance of experiencing sleep inertia. Adenosine levels in the brain progressively increase with sleep deprivation, and return to normal during sleep. Upon awakening with sleep deprivation, high amounts of adenosine will be bound to receptors in the brain, neural activity slows down, and a feeling of tiredness will result. Studies show that individuals express a lack of blood flow to the brain upon awakening. Levels of cerebral blood flow (CBF) and cerebral blood flow velocities (CBFV) will take up to 30 minutes to increase and reach daytime levels. Studies using advanced imaging have shown that cerebral blood flow will return to waking levels in the brainstem and thalamus first. Then, after 15 minutes, the brains anterior cortical regions receive normal daytime blood flow. This 15 minute time period corresponds to the sleep inertia period. Studies show that drinking alcoholic beverages in the evening causes physiological distress upon wake up. This phenomenon is known colloquially as a hangover.
Treatments / countermeasures
There has been a great deal of research into potential methods to relieve the effects of sleep inertia. The demand for remedies is driven by the occupational hazards of sleep inertia for employees who work extended shifts such as medical professionals, emergency responders, or military personnel. The motor functioning and cognitive ability of these professionals who must immediately respond to a call can pose a safety hazard in the workplace. Below are some of the various methods that have been suggested to combat sleep inertia. Napping
When a person is sleep deprived, re-entering sleep may provide a viable route to reduce mental and physical fatigue but it can also induce sleep inertia. In order to limit sleep inertia, one should avoid waking from the deeper stages of slow-wave sleep. The onset of slow-wave sleep occurs approximately 30 minutes after falling asleep, therefore a nap should be limited to under 30 minutes to prevent waking during slow-wave sleep and enhancing sleep inertia. Furthermore, self-awakening from a short nap was shown to relieve disorientation of sleep inertia as opposed to a forced awakening, but these results may warrant more research into the nature of arousal after sleep periods. Caffeine
Caffeine is a xanthine derivative that can cross the blood-brain barrier. The caffeine present in coffee or tea exerts its stimulating action by blocking adenosine receptors in the brain. By antagonizing the adenosine receptors caffeine limits the effects of adenosine buildup in the brain and increases alertness and attentiveness.