In addition, an evidence-based synopses suggests that the sleep disorder, idiopathic REM sleep behavior disorder (iRBD), may have a hereditary component to it. A total of 632 participants, half with iRBD and half without, completed self-report questionnaires. The results of the study suggest that people with iRBD are more likely to report having a first-degree relative with the same sleep disorder than people of the same age and sex that do not have the disorder.[19] More research needs to be conducted to gain further information about the hereditary nature of sleep disorders.
Recent studies, however, have shown that several factors can interrupt this neurogenesis.[29] These include stress and prolonged sleep deprivation (more than one day).[29] The sleep disturbances encountered in AD could therefore suppress neurogenesis and thus impairing hippocampal functions.[29] This would therefore contribute to diminished memory performances and the progression of AD.[29] And progression of AD would aggravate sleep disturbances.[29] It is a second vicious circle.  
Delayed sleep phase disorder (DSPD), inability to awaken and fall asleep at socially acceptable times but no problem with sleep maintenance, a disorder of circadian rhythms. Other such disorders are advanced sleep phase disorder (ASPD), non-24-hour sleep–wake disorder (non-24) in the sighted or in the blind, and irregular sleep wake rhythm, all much less common than DSPD, as well as the situational shift work sleep disorder.[4]
"has demonstrated expertise in the diagnosis and management of clinical conditions that occur during sleep, that disturb sleep, or that are affected by disturbances in the wake-sleep cycle. This specialist is skilled in the analysis and interpretation of comprehensive polysomnography, and well-versed in emerging research and management of a sleep laboratory."[51]
Primary sleep disorders are most common in men and women over the age of 65. About half of the people claim to have some sleep problem at one point. It is most common in the elderly because of multiple factors. Factors include increased medication use, age-related changes in circadian rhythms, environmental and lifestyle changes [3] and pre diagnosed physiological problems and stress. The risk of developing sleep disorders in the elderly is especially increased for sleep disordered breathing, periodic limb movements, lestless legs syndrome, REM sleep behavior disorders, insomnia and circadian rhythm disturbances.[3]

^ Hirshkowitz, Max (2004). "Chapter 10, Neuropsychiatric Aspects of Sleep and Sleep Disorders (pp 315-340)" (Google Books preview includes entire chapter 10). In Stuart C. Yudofsky; Robert E. Hales (eds.). Essentials of neuropsychiatry and clinical neurosciences (4 ed.). Arlington, Virginia, USA: American Psychiatric Publishing. ISBN 978-1-58562-005-0. ...insomnia is a symptom. It is neither a disease nor a specific condition. (from p. 322)
Combining results from 17 studies on insomnia in China, a pooled prevalence of 15.0% is reported for the country.[60] This is considerably lower than a series of Western countries (50.5% in Poland, 37.2% in France and Italy, 27.1% in USA).[60] However, the result is consistent among other East Asian countries. Men and women residing in China experience insomnia at similar rates.[60] A separate meta-analysis focusing on this sleeping disorder in the elderly mentions that those with more than one physical or psychiatric malady experience it at a 60% higher rate than those with one condition or less. It also notes a higher prevalence of insomnia in women over the age of 50 than their male counterparts.[61]
Another systematic review noted 7-16% of young adults suffer from delayed sleep phase disorder. This disorder reaches peak prevalence when people are in their 20s.[57] Between 20 and 26% of adolescents report a sleep onset latency of >30 minutes. Also, 7-36% have difficulty initiating sleep.[59] Asian teens tend to have a higher prevalence of all of these adverse sleep outcomes than their North American and European counterparts.[59]
Delayed sleep phase disorder is a condition where your biological clock is significantly delayed. As a result, you go to sleep and wake up much later than other people. This is more than just a preference for staying up late or being a night owl, but rather a disorder that makes it difficult for you to keep normal hours—to make it to morning classes, get the kids to school on time, or keep a 9-to-5 job.
If sleeping with a mask on doesn't work for you, other options are surgery; oral appliances; and newer, minimally invasive outpatient surgical treatments. These include the Pillar procedure, which involves using permanent stitches to firm up the soft palate; coblation, which uses radiofrequency to shrink nasal tissues; and even use of a carbon dioxide laser to shrink the tonsils.