Currently, the International Classification of Sleep Disorders (ICSD-3) lists 6 disorders under the category of<unk> s.<unk> s can be categorized into two groups based on their underlying mechanisms: The first category is composed of disorders where the endogenous oscillator has been altered, known as intrinsic type disorders. The second category consists of disorders in which the external environment and the endogenous<unk>  clock are misaligned, called extrinsic type<unk> s. Intrinsic * Delayed sleep phase disorder (DSPD): Individuals who have been diagnosed with delayed sleep phase disorder have sleep-wake times which are delayed when compared to normal functioning individuals. People with DSPD typically have very long periods of sleep latency when they attempt to go to sleep during conventional sleeping times. Similarly, they also have trouble waking up at conventional times. * Advanced sleep phase disorder (ASPD): People with advanced sleep phase disorder exhibit characteristics opposite to those with delayed sleep phase disorder. These individuals have advanced sleep wake times, so they tend to go to bed and wake up much earlier as compared to normal individuals. ASPD is less common than DSPD, and is most prevalent within older populations. * Familial Advanced Sleep Phase Syndrome (FASPS) is linked to an autosomal dominant mode of inheritance. It is associated with a missense mutation in human PER2 that replaces Serine for a Glycine at position 662 (S662G). Families that have this mutation in PER2 experience extreme phase advances in sleep, waking up around 2 AM and going to bed around 7 PM. * Irregular sleep–wake<unk>  disorder (ISWRD) is characterized by a normal 24-hr sleeping period. However, individuals with this disorder experience fragmented and highly disorganized sleep that can manifest in the form of waking frequently during the night and taking naps during the day, yet still maintaining sufficient total time asleep. People with ISWRD often experience a range of symptoms from insomnia to excessive daytime sleepiness. * Non-24-hour sleep–wake disorder (N24SWD): Most common in individuals that are blind and unable to detect light, is characterized by chronic patterns of sleep/wake cycles which are not entrained to the 24-hr light-dark environmental cycle. As a result of this, individuals with this disorder will usually experience a gradual yet predictable delay of sleep onset and waking times. Patients with DSPD may develop this disorder if their condition is untreated. Extrinsic * Shift work sleep disorder (SWSD): Approximately 9% of Americans who work night or irregular work shifts are believed to experience Shift work sleep disorder. Night shift work directly opposes the environmental cues that entrain our biological clock, so this disorder arises when an individual's clock is unable to adjust to the socially imposed work schedule. Shift work sleep disorder can lead to severe cases of insomnia as well as excessive daytime sleepiness. * Jet lag: Jet lag is best characterized by difficulty falling asleep or staying asleep as a result of misalignment between one's internal<unk>  system and external, or environmental cues. It is typically associated with rapid travel across multiple time zones.
Circadian rhythm sleep disorder
Non-24-hour sleep–wake disorder
Shift work sleep disorder
Delayed sleep phase disorder
Advanced sleep phase disorder
Sleep disorder
Rapid eye movement sleep behavior disorder
Sleep state misperception