Circadian Rhythm Sleep-Wake Disorders 391
307.45 (G47.24) Non-24-hour sleep-wake type:  A pattern of sleep-wake cycles that
is not synchronized to the 24-hour environment, with a consistent daily drift (usually to
later and later times) of sleep onset and wake times.
307.45 (G47.26) Shift work type:  Insomnia during the major sleep period and/or ex-
cessive sleepiness (including inadvertent sleep) during the major awake period asso-
ciated with a shift work schedule (i.e., requiring unconventional work hours).
307.45 (G47.20) Unspecified type
Specify if:
Episodic:  Symptoms last at least 1 month but less than 3 months.
Persistent:  Symptoms last 3 months or longer.
Recurrent: Two or more episodes occur within the space of 1 year.
Delayed Sleep Phase Type
Diagnostic Features
The delayed sleep phase type is based primarily on a history of a delay in the timing of the
major sleep period (usually more than 2 hours)  in relation to the desired sleep and wake-
up time, resulting in symptoms of insomnia and excessive sleepiness. When allowed to set
their own schedule, individuals with delayed sleep phase type exhibit normal sleep qual-
ity and duration for age. Symptoms of slee p-onset insomnia, diffic ulty waking in the
morning, and excessive early day sleepiness are prominent.
Associated Features Supporting Diagnosis
Common associated features of delayed sleep phase type include a hi story of mental dis-
orders or a concurrent mental disorder. Ex treme and prolonged difficulty awakening with
morning confusion is also common. Psychophy siological insomnia may develop as a re-
sult of maladaptive behaviors that impair sleep and increase arousal because of repeated