At the same time, it has been shown that memory consolidation in long-term memory (which depends on the hippocampus) occurs during NREM sleep. 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. This drop in performance is one of the central symptoms of AD.
In Alzheimer's disease, in addition to cognitive decline and memory impairment, there is also significant sleep disturbances with a modified sleep architecture. The latter may consist in sleep fragmentation, a reduction in sleep duration, insomnia, an increase daytime naping, a decreased quantity og some sleep stages and a resemblance between some sleep stages (N1 and N2). More than 65% of people with Alzheimer's disease suffer from this type of sleep disturbance.
Narcolepsy is characterized by “sleep attacks” that occur during the day. This means that you will suddenly feel extremely tired and fall asleep without warning. The disorder can also cause sleep paralysis, which may make you physically unable to move right after waking up. Although narcolepsy may occur on its own, it is also associated with certain neurological disorders, such as multiple sclerosis.
Restless legs syndrome (RLS) is a sleep disorder that causes an almost irresistible urge to move your legs (or arms) at night. The urge to move occurs when you’re resting or lying down and is usually due to uncomfortable, tingly, aching, or creeping sensations. There are plenty of ways to help manage and relieve symptoms, though, including self-help remedies you can use at home.
Narcolepsy is a brain disorder that causes excessive daytime sleepiness. There is sometimes a genetic component, but most patients have no family history of the problem. Though dramatic and uncontrolled "sleep attacks" have been the best-known feature of narcolepsy, in reality many patients do not have sleep attacks. Instead, they experience constant sleepiness during the day.
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  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.