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.
The mean T1/2 is 20.7 hours. The decanoate injectable formulation is for intramuscular administration only and is not intended to be used intravenously. The plasma concentrations of haloperidol decanoate reach a peak at about six days after the injection, falling thereafter, with an approximate half-life of three weeks. Intravenous injections
The bioavailability is 100% in intravenous (IV) injection, and the very rapid onset of action is seen within seconds. The T1/2 is 14.1 to 26.2 hours. The apparent volume of distribution is between 9.5 and 21.7 L/kg. The duration of action is four to six hours. Therapeutic concentrations
Plasma levels of five to 15 micrograms per liter are typically seen for therapeutic response (Ulrich S, et al. Clin Pharmacokinet. 1998). The determination of plasma levels is rarely used to calculate dose adjustments but can be useful to check compliance. The concentration of haloperidol in brain tissue is about 20-fold higher compared to blood levels. It is slowly eliminated from brain tissue,  which may explain the slow disappearance of side effects when the medication is stopped. Distribution and metabolism
Haloperidol is heavily protein bound in human plasma, with a free fraction of only 7.5 to 11.6%. It is also extensively metabolized in the liver with only about 1% of the administered dose excreted unchanged in the urine. The greatest proportion of the hepatic clearance is by glucuronidation, followed by reduction and CYP-mediated oxidation, primarily by CYP3A4. History
Haloperidol was discovered by Paul Janssen.