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 rhythm 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.
Melatonin, a naturally occurring biological hormone with circadian rhythmicity, has been shown to promote sleep and entrainment to external cues when administered in drug form (0.5–5.0 mg). Melatonin administered in the evening causes phase advances in sleep-wake times while maintaining duration and quality of sleep. Similarly, when administered in the early morning, melatonin can cause phase delays. It has been shown most effective in cases of shift work sleep disorder and delayed phase sleep disorder, but has not been proven particularly useful in cases of jet lag. Dark therapy, for example, the use of blue-blocking goggles, is used to block blue and blue-green wavelength light from reaching the eye during evening hours so as not to hinder melatonin production. See also
References
External links

Circadian Sleep Disorders Network
An American Academy of Sleep Medicine Review: Circadian Rhythm Sleep Disorders: Part I, Basic Principles, Shift Work and Jet Lag Disorders. PDF, 24 pages. November 2007. An American Academy of Sleep Medicine Review: Circadian Rhythm Sleep Disorders: Part II, Advanced Sleep Phase Disorder, Delayed Sleep Phase Disorder, Free-Running Disorder, and Irregular Sleep–Wake Rhythm. PDF, 18 pages. November 2007. An American Academy of Sleep Medicine Report: Practice Parameters for the Clinical Evaluation and Treatment of Circadian Rhythm Sleep Disorders, November 1, 2007
NASA Sleep–Wake Actigraphy and Light Exposure During Spaceflight-Long Experiment