Non-24-hour sleep–wake disorder
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Non-24-hour sleep–wake disorder Other names Hypernychthemeral syndrome, free-running disorder Specialty Neurology Symptoms Progressively shifting nighttime Complications None if sleeping according to biological clock, sleep deprivation otherwise Duration Lifetime Causes Blindness for the blind, unknown cause for the sighted Diagnostic method Sleep diary, actigraphy Treatment Medication Medication Tasimelteon, Melatonin Frequency 55–70% of total blind people, less prevalent in sighted

Non-24-hour sleep–wake disorder (non-24[1] or N24SWD[2]) is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in society".[3] Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light/dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind, it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder, depression, and traumatic brain injury.[2] The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.[2][4]

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Sighted [ edit ]

In people with non-24, the body essentially insists that the length of a day (and night) is appreciably longer (or, very rarely, shorter) than 24 hours and refuses to adjust to the external light–dark cycle. This makes it impossible to sleep at normal times and also causes daily shifts in other aspects of the circadian rhythm such as peak time of alertness, body temperature minimum, metabolism and hormone secretion. Non-24-hour sleep–wake disorder causes a person's sleep–wake cycle to move around the clock every day, to a degree dependent on the length of the cycle, eventually returning to "normal" for one or two days before "going off" again. This is known as free-running sleep.

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