Hypersomnia is a neurological disorder of excessive time spent sleeping or excessive sleepiness. It can have many possible causes (such as seasonal affective disorder) and can cause distress and problems with functioning. In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), hypersomnolence, of which there are several subtypes, appears under sleep-wake disorders. Hypersomnia is a pathological state characterized by a lack of alertness during the waking episodes of the day. It is not to be confused with fatigue, which is a normal physiological state. Daytime sleepiness appears most commonly during situations where little interaction is needed. Since the patients’ attention levels (wakefulness) are impaired, their quality of life may be impacted as well. This is especially true for people whose jobs request high levels of attention, such as in the healthcare field. Symptoms The main symptom of hypersomnia is excessive daytime sleepiness (EDS), or prolonged nighttime sleep, which has occurred for at least 3 months prior to diagnosis. Sleep drunkenness is also a symptom found in hypersomniac patients. It is a difficulty transitioning from sleep to wake. Individuals experiencing sleep drunkenness report waking with confusion, disorientation, slowness and repeated returns to sleep. It also appears in non-hypersomniac persons, for example after a night of insufficient sleep. Fatigue and consumption of alcohol or hypnotics can cause sleep drunkenness as well. It is also associated with irritability: people who get angry shortly before sleeping tend to experience sleep drunkenness. According to the American Academy of Sleep Medicine, hypersomniac patients often take long naps during the day that are mostly unrefreshing. Researchers found that naps are usually more frequent and longer in patients than in controls. Furthermore, 75% of the patients report that short naps are not refreshing, compared to controls. Diagnosis "The severity of daytime sleepiness needs to be quantified by subjective scales (at least the Epworth Sleepiness Scale) and objective tests such as the multiple sleep latency test (MSLT)." The Stanford sleepiness scale (SSS) is another frequently-used subjective measurement of sleepiness. After it is determined that excessive daytime sleepiness is present, a complete medical examination and full evaluation of potential disorders in the differential diagnosis (which can be tedious, expensive and time-consuming) should be undertaken. Differential diagnosis Hypersomnia can be primary (of central/brain origin), or it can be secondary to any of numerous medical conditions. More than one type of hypersomnia can coexist in a single