The dyssomnia not otherwise specified category is for insomnias, hypersomnias, or circadian rhythm disturbances that do not meet criteria for any specific dyssomnia. Examples include

1. Complaints of clinically significant insomnia or hypersomnia that are attributable to environmental factors (e.g., noise, light, frequent interruptions).
2. Excessive sleepiness that is attributable to ongoing sleep deprivation.
3. “Restless legs syndrome”: This syndrome is characterized by a desire to move the legs or arms, associated with uncomfortable sensations typically described as creeping, crawling, tingling, burning, or itching. Frequent movements of the limbs occur in an effort to relieve the uncomfortable sensations. Symptoms are worse when the individual is at rest and in the evening or night, and they are relieved temporarily by movement. The uncomfortable sensations and limb movements can delay sleep onset, awaken the individual from sleep, and lead to daytime sleepiness or fatigue. Sleep studies demonstrate involuntary periodic limb movements during sleep in a majority of individuals with restless legs syndrome. A minority of individuals have evidence of anemia or reduced serum iron stores. Peripheral nerve electrophysiological studies and gross brain morphology are usually normal. Restless legs syndrome can occur in an idiopathic form, or it can be associated with general medical or neurological conditions, including normal pregnancy, renal failure, rheumatoid arthritis, peripheral vascular disease, or peripheral nerve dysfunction. Phenomenologically, the two forms are indistinguishable. The onset of restless legs syndrome is typically in the second or third decade, although up to 20% of individuals with this syndrome may have symptoms before age 10. The prevalence of restless legs syndrome is between 2% and 10% in the general population and as high as 30% in general medical populations. Prevalence increases with age and is equal in males and females. Course is marked by stability or worsening of symptoms with age. There is a positive family history in 50%–90% of individuals. The major differential diagnoses include medication-induced akathisia, peripheral neuropathy, and nocturnal leg cramps. Worsening at night and periodic limb movements are more common in restless legs syndrome than in medication-induced akathisia or peripheral neuropathy. Unlike restless legs syndrome, nocturnal leg cramps do not present with the desire to move the limbs nor are there frequent limb movements.
4. Periodic limb movements: Periodic limb movements are repeated low-amplitude brief limb jerks, particularly in the lower extremities. These movements begin near sleep onset and decrease during stage 3 or 4 non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. Movements usually occur rhythmically every 20–60 seconds and are associated with repeated, brief arousals. Individuals are often unaware of the actual movements, but may complain of insomnia, frequent awakenings, or daytime sleepiness if the number of movements is very large. Individuals may have considerable variability in the number of periodic limb movements from night to night. Periodic limb movements occur in the majority of individuals with restless legs syndrome, but they may also occur without the other symptoms of restless legs syndrome. Individuals with normal pregnancy or with conditions such as renal failure, congestive heart failure, and posttraumatic stress disorder may also develop periodic limb movements. Although typical age at onset and prevalence in the general population are unknown, periodic limb movements increase with age and may occur in more than one-third of individuals over age 65. Men are more commonly affected than women.
5. Situations in which the clinician has concluded that a dyssomnia is present but is unable to determine whether it is primary, due to a general medical condition, or substance induced.