the clinically comorbid conditions. A concurre nt insomnia diagnosis should only be con-
sidered when the insomnia is sufficiently severe  to warrant independent clinical attention;
otherwise, no separate diagnosis is necessary.
Diagnostic Features
The essential feature of insomnia disorder is dissatisfaction with sleep quantity or quality
with complaints of difficulty initiating or maintaining sleep. The sleep complaints are ac-
companied by clinically significant distress or  impairment in social, occupational, or other
important areas of functioning. The sleep dist urbance may occur during the course of an-
other mental disorder or medical condition, or it  may occur independently.
Different manifestations of insomnia can oc cur at different times of the sleep period. Sleep-
onset insomnia  (or initial insomnia ) involves difficulty initia ting sleep at bedtime. Sleep mainte-
nance insomnia  (or middle insomnia ) involves frequent or prol onged awakenings throughout
the night. Late insomnia involves early-morning awakening with an inability to return to sleep.
Difficulty maintaining sleep is the most co mmon single symptom of insomnia, followed by
difficulty falling asleep, while a combination of  these symptoms is th e most common presen-
tation overall. The specific type of sleep comp laint often varies over time. Individuals who
complain of difficulty falling asleep at one time may later complain of difficulty maintaining
sleep, and vice versa. Symptoms of difficulty falling asleep and difficulty maintaining sleep
can be quantified by the individual’s retrospect ive self-report, sleep di aries, or other methods,
such as actigraphy or polysomnography, but th e diagnosis of insomnia disorder is based on
the individual’s subjecti ve perception of sleep or a caretaker’s report. 
Nonrestorative sleep,  a complaint of poor sleep quality that does not leave the individual
rested upon awakening despite adequate du ration, is a common sleep complaint usually