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 brain's 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. Previous research has shown that coupled with a short nap, consuming caffeine prior to the nap can alleviate the effects of sleep inertia. Nonetheless, individual degree of consumption and tolerance to caffeine may be responsible for variation in its efficacy to reduce sleep inertia symptoms. Light The natural light provided by the sunrise may contribute to a reduction in sleep inertia