Sleep inertia is a physiological state of impaired cognitive and sensory-motor performance that is present immediately after awakening. It persists during the transition of sleep to wakefulness, where an individual will experience feelings of drowsiness, disorientation and a decline in motor dexterity. Impairment from sleep inertia may take several hours to dissipate. In the majority of cases, morning sleep inertia is experienced for 15 to 30 minutes after waking. Sleep inertia is of concern with decision-making abilities, safety-critical tasks and the ability to operate efficiently soon after awakening. In these situations, it poses an occupational hazard due to the cognitive and motor deficits that may be present. Symptoms "Grogginess", as defined by a drowsy or disoriented state in which there is a dampening of sensory acuity and mental processing. Impaired motor dexterity and decrease in cognitive ability. These gross impairments may be responsible for the associated increase in reaction time and drop in attentiveness. Deficits in spatial memory Reports of heightened subjective fatigue These symptoms are expressed with the greatest intensity immediately after waking, and dissipate following a period of extended wakefulness. The duration of symptoms varies on a conditional basis, with primary expression during the first 15–60 minutes after waking and potentially extending for several hours. Tasks that require more complex cognitive operations will feature greater deficits as compared to a simple motor task; the accuracy of sensory and motor functioning is more impaired by sleep inertia as compared to sheer speed. 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