Sleep disturbances have been also observed in Alzheimer's disease (AD), affecting about 45% of its population.[22][24][26] Moreover, when it is based on caregiver reports this percentage is even higher, about 70%.[28] As well as in PD population, insomnia and hypersomnia are frequently recognized in AD patients, which have been associated with accumulation of Beta-amyloid, circadian rhythm sleep disorders (CRSD) and melatonin alteration.[22][24][28] Additionally, changes in sleep architecture are observed in AD too.[22][24][26] Even though with ageing the sleep architecture seems to change naturally, in AD patients it is aggravated. SWS is potentially decreased (sometimes totally absent), spindles and the time spent in REM sleep are also reduced, while its latency is increased.[28] The poorly sleep onset in AD has been also associated with dream-related hallucination, increased restlessness, wandering and agitation, that seem to be related with sundowning - a typical chronological phenomenon presented in the disease.[24][28]
In addressing sleep disorders and possible solutions, there is often a lot of buzz surrounding melatonin. Research suggests that melatonin is useful in helping people to fall asleep faster (decreased sleep latency), to stay asleep longer, and to experience improved sleep quality. In order to test this, a study was conducted that compared subjects that had taken Melatonin to subjects that had taken a placebo pill in subjects with primary sleep disorders. Researchers assessed sleep onset latency, total minutes slept, and overall sleep quality in the Melatonin and placebo groups to note the differences. In the end, researchers found that melatonin decreased sleep onset latency, increased total sleep time, and improved quality of sleep significantly more than the placebo group.[49][50]
A population susceptible to the development of sleep disorders is people who have experienced a traumatic brain injury (TBI). Because many researchers have focused on this issue, a systematic review was conducted to synthesize their findings. According to their results, TBI individuals are most disproportionately at risk for developing narcolepsy, obstructive sleep apnea, excessive daytime sleepiness, and insomnia.[20] The study's complete findings can be found in the table below:

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."
A nocturnal movement disorder, restless leg syndrome can feel like itchiness, tingling, or prickling that makes you feel like you have to move your legs. Your legs may also move without your control while you sleep. You may or may not be aware of waking during the night, but restless leg syndrome causes sleep problems by preventing deep, restful sleep.

Waking up in the middle of the night to use the bathroom is such a common problem it has a name: nocturia . As we get older, our bodies' ability to hold fluids for long periods decreases, thanks to a decline in antidiuretic hormones. According to the National Sleep Foundation, 65 percent of older adults have sleep deprivation resulting from waking up frequently to use the bathroom.