Which of the following is a dyssomnia sleep disorder?

Insomnia is classified as a dyssomnia sleep disorder because it pertains to problems with the amount, quality, or timing of sleep. Dyssomnias are characterized by difficulty in initiating or maintaining sleep, excessive sleepiness, or altered sleep cycles. Insomnia specifically involves difficulty falling asleep, staying asleep, or waking up too early and not being able to return to sleep, leading to significant distress or impairment in daytime functioning.

In contrast, nightmares are classified as parasomnias, which involve abnormal movements, behaviors, or experiences during sleep. Sleepwalking, another type of parasomnia, occurs during non-REM sleep and typically involves the individual walking or performing other complex behaviors while still asleep. Sleep apnea, while also a serious condition affecting sleep quality, is a sleep-related breathing disorder rather than a dyssomnia, as it involves interruptions in breathing during sleep, which may lead to poor sleep quality without the primary issue being the initiation or maintenance of sleep itself.