to combat excessive fatigue. In addition to worsening the insomnia, this type of substance
use may in some cases progress to a substance use disorder.
Relationship to Internat ional Classification of 
Sleep Disorders
There are several distinct inso mnia phenotypes relating to the perceived source of the in-
somnia that are recognized by the International Classifica tion of Sleep Disorders,  2nd Edition
(ICSD-2). These include psychophysiological insomnia,  idiopathic insomnia,  sleep-state mispercep-
tion, and inadequate sleep hygiene.  Despite their clinical appeal and heuristic value, there is
limited evidence to support these distinct phenotypes.
Hypersomnolence Disorder
Diagnostic Criteria 307.44 (F51.11)
A. Self-reported excessive sleepiness (hypersomnolence) despite a main sleep period
lasting at least 7 hours, with at least one of the following symptoms: 
1. Recurrent periods of sleep or lapses into sleep within the same day.
2. A prolonged main sleep episode of more than 9 hours per day that is nonrestorative
(i.e., unrefreshing).
3. Difficulty being fully awake after abrupt awakening.
B. The hypersomnolence occurs at least three times per week, for at least 3 months.
C. The hypersomnolence is accompanied by si gnificant distress or impairment in cogni-
tive, social, occupational, or other important areas of functioning. 
D. The hypersomnolence is not better explai ned by and does not occur exclusively during
the course of another sleep disorder (e.g., narcolepsy, breathing-related sleep disor-
der, circadian rhythm sleep-wake disorder, or a parasomnia).
E. The hypersomnolence is not attributable to the physiological effects of a substance