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]
The neurodegenerative conditions are commonly related to brain structures impairment, which might disrupt the states of sleep and wakefulness, circadian rhythm, motor or non motor functioning.[22][24] On the other hand, sleep disturbances are also frequently related to worsening patient's cognitive functioning, emotional state and quality of life.[24][27][28] Furthermore, these abnormal behavioural symptoms negatively contribute to overwhelming their relatives and caregivers.[24][27][28] Therefore, a deeper understanding of the relationship between sleep disorders and neurodegenerative diseases seems to be extremely important, mainly considering the limited research related to it and the increasing expectancy of life.[22][28]
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 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.
As suggested by its name, PLMD is an involuntary movement disorder. (An older name, nocturnal myoclonus , is rarely used anymore.) People with this problem experience sudden, involuntary leg movements during the night, such as kicking or jerking. The difference between this and restless leg syndrome is that, unless the kicking wakes you up, you don't know you're doing it. You don't experience the tingling and discomfort that leads you to consciously move your legs, as with restless leg syndrome. At least 80 percent of people with restless leg syndrome have PLMD, but the reverse isn't true.
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.
Frequently having trouble sleeping can be a frustrating and debilitating experience. You sleep badly at night, which leaves you feeling dead-tired in the morning and whatever energy you have quickly drains throughout the day. But then, no matter how exhausted you feel at night, you still have trouble sleeping. And so the cycle begins again, taking a serious toll on your mood, energy, efficiency, and ability to handle stress. Ignoring sleep problems and disorders can damage your physical health and lead to weight gain, car accidents, impaired job performance, memory problems, and strained relationships. If you want to feel your best, stay healthy, and perform up to your potential, quality sleep is a necessity, not a luxury.
One factors that could explain this change in sleep architecture is a change in circadian rhythm, which regulates sleep.[29] A disruption of the circadian rhythm would therefore generate sleep disturbances.[29] Some studies show that people with AD have a delayed circadian rhythm, whereas in normal aging we will find an advanced circadian rhythm.[29][31]
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.
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