in DSM–IV–TR, a primary sleep disorder marked by excessive sleepiness or insomnia arising from sleep disruption due to breathing difficulties during sleep, for example, sleep apnea. In DSM–5, the classification refers to three specific disorders: obstructive sleep apnea hypopnea (characterized by episodes of absent or reduced breathing during sleep and by daytime sleepiness); central sleep apnea (repeated episodes of absent or reduced breathing caused by variability in respiratory control during sleep); and sleep-related hypoventilation (decreased respiration during sleep). See dyssomnia.