People who have insomnia don't feel as if they get enough sleep at night. They may have trouble falling asleep or may wake up frequently during the night or early in the morning. Insomnia is a problem if it affects your daytime activities. Insomnia has many possible causes, including stress, anxiety, depression, poor sleep habits, circadian rhythm disorders (such as jet lag), and taking certain medications.
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.
Fatigue during the first trimester of pregnancy is likely caused by changing levels of hormones, such as progesterone. Toward the end of pregnancy, some women find it difficult to sleep because of the uncomfortable size of their abdomen. Some women are too excited, anxious, or worried about becoming mothers to sleep well. Other women who are pregnant complain that vivid dreams prevent them from getting restful sleep. Sleep apnea, especially if it's severe and causes your blood oxygen level to drop during sleep, is a risk to the fetus.
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.
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. On the other hand, sleep disturbances are also frequently related to worsening patient's cognitive functioning, emotional state and quality of life. Furthermore, these abnormal behavioural symptoms negatively contribute to overwhelming their relatives and caregivers. 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.
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.)