A. The predominant complaint is excessive sleepiness for at least 1 month (or less if recurrent) as evidenced by either prolonged sleep episodes or daytime sleep episodes that occur almost daily.

B. The excessive sleepiness causes clinically significant distress or impairment in social, occupational, or other important areas of functioning.

C. The excessive sleepiness is not better accounted for by Insomnia and does not occur exclusively during the course of another Sleep Disorder (e.g. Narcolepsy, Breathing-Related Sleep Disorder, Circadian Rhythm Sleep Disorder, or a Parasomnia) and cannot be accounted for by an inadequate amount of sleep.

D. The disturbance does not occur exclusively during the course of another mental disorder.

E. The disturbance is not due to the direct physiological effects of a substance (e.g. a drug of abuse, a medication) or a general medical condition.

Specify if:
Recurrent: if there are periods of excessive sleepiness that last at least 3 days occurring several times a year for at least 2 years

Based on the Diagnostic & Statistical Manual of Mental Disorders, 4th edition APA

Also: Hypersomnia Related to Another Mental Disorder

The online Diagnostic & Statistical Manual of Mental Disorders lists most of the major psychological disorders and illnesses and lists the criteria that must be fulfilled in order for a diagnosis to be made. This resource is not a substitute for proper professional psychiatric diagnosis.