Now consider noise. If a ticking clock disturbs you, buy one that doesn't tick, or use your phone. Turn clock radios and MP3 players to the wall and cover lighted screens. Lay in supplies of earplugs, eye masks, and anything else that helps screen out light as well as sound. Some people find a fan or white-noise machine is soothing and blocks out street noise. If you don't like wearing earplugs or an eye mask when you fall asleep, keep them on your bedside table in case you wake up later. Many people find they're more sensitive to light and sound in the middle of the night.
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]
^ 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)

Competence in sleep medicine requires an understanding of a myriad of very diverse disorders, many of which present with similar symptoms such as excessive daytime sleepiness, which, in the absence of volitional sleep deprivation, "is almost inevitably caused by an identifiable and treatable sleep disorder", such as sleep apnea, narcolepsy, idiopathic hypersomnia, Kleine–Levin syndrome, menstrual-related hypersomnia, idiopathic recurrent stupor, or circadian rhythm disturbances.[52] Another common complaint is insomnia, a set of symptoms which can have a great many different causes, physical and mental. Management in the varying situations differs greatly and cannot be undertaken without a correct diagnosis.[citation needed]

Apnea means "no airflow." Obstructive sleep apnea was thought to be a disorder primarily of overweight, older men. But abnormal breathing during sleep can affect people of any age, any weight, and either sex. Researchers now know that in many cases of sleep apnea, the obstruction in the airways is only partial. Most people with sleep apnea have a smaller-than-normal inner throat and other subtle bone and soft-tissue differences.
Throughout the decades as more research and studies were conducted, the amount of sleep disorders being discovered began to rapidly increase. In 1990 The AASM, along with other professional societies including the European Sleep Research Society, The Japanese Society of Sleep Research, and the Latin American Sleep Society published the International Classification of Sleep Disorders (ICSD), which is a "primary diagnostic, epidemiological, and coding resource for clinicians and researchers in the field of sleep and sleep medicine."
At the same time, it has been shown that memory consolidation in long-term memory (which depends on the hippocampus) occurs during NREM sleep.[29][33] This indicates that a decrease in the NREM sleep will result in less consolidation and therefore poorer memory performances in hippocampal-dependent long-term memory.[29][33] This drop in performance is one of the central symptoms of AD.[29]  

A systematic review found that traumatic childhood experiences (such as family conflict or sexual trauma) significantly increases the risk for a number of sleep disorders in adulthood, including sleep apnea, narcolepsy, and insomnia.[17] It is currently unclear whether or not moderate alcohol consumption increases the risk of obstructive sleep apnea.[18]

Keep a pen and paper next to your bed. If you're often kept awake by racing thoughts and worries and you tend to make to-do lists in your head, keep a pen or pencil and a small pad of paper handy and write them down. As you put each item down on paper, imagine yourself setting aside that concern. (Again, use a book light; don't turn on the overhead or a bright bedside light to write.)