Because their perception of their sleep is incomplete, they incorrectly believe it takes them an abnormally long time to fall asleep, and they underestimate how long they remain asleep. Causes
Symptoms of insomnia can be caused by or be associated with:

Sleep breathing disorders, such as sleep apnea or upper airway resistance syndrome
Use of psychoactive drugs (such as stimulants), including certain medications, herbs, caffeine, nicotine, cocaine, amphetamines, methylphenidate, aripiprazole, MDMA, modafinil, or excessive alcohol intake
Use of or withdrawal from alcohol and other sedatives, such as anti-anxiety and sleep drugs like benzodiazepines
Use of or withdrawal from pain-relievers such as opioids
Heart disease
Restless legs syndrome, which can cause sleep onset insomnia due to the discomforting sensations felt and the need to move the legs or other body parts to relieve these sensations
Periodic limb movement disorder (PLMD), which occurs during sleep and can cause arousals of which the sleeper is unaware
Pain: an injury or condition that causes pain can preclude an individual from finding a comfortable position in which to fall asleep, and can also cause awakening.
Rates of use were lowest among the youngest age group (those aged 20–39) at about 2%, increased to 6% among those aged 50–59, and reached 7% among those aged 80 and over. More adult women (5%) reported using prescription sleep aids than adult men (3%). Non-Hispanic white adults reported higher use of sleep aids (5%) than non-Hispanic black (3%) and Mexican-American (2%) adults. No difference was shown between non-Hispanic black adults and Mexican-American adults in use of prescription sleep aids. Antihistamines
As an alternative to taking prescription drugs, some evidence shows that an average person seeking short-term help may find relief by taking over-the-counter antihistamines such as diphenhydramine or doxylamine. Diphenhydramine and doxylamine are widely used in nonprescription sleep aids. They are the most effective over-the-counter sedatives currently available, at least in much of Europe, Canada, Australia, and the United States, and are more sedating than some prescription hypnotics. Antihistamine effectiveness for sleep may decrease over time, and anticholinergic side-effects (such as dry mouth) may also be a drawback with these particular drugs. While addiction does not seem to be an issue with this class of drugs, they can induce dependence and rebound effects upon abrupt cessation of use. However, people whose insomnia is caused by restless legs syndrome may have worsened symptoms with antihistamines. Antidepressants
While insomnia is a common symptom of depression, antidepressants are effective for treating sleep problems whether or not they are associated with depression.