Which of the following is an example of parasomnia?

Parasomnias are abnormal behaviors or events that occur during sleep, often involving undesirable physical or verbal events. Nightmares, in particular, are vivid and often disturbing dreams that can lead to awakening and distress. They typically occur during REM (rapid eye movement) sleep and can leave the individual feeling anxious or upset.

While the other options may relate to sleep disturbances, they do not fit the definition of parasomnia as directly as nightmares do. Scenarios of sleep apnea refer to a sleep disorder characterized by interrupted breathing and do not involve abnormal behaviors. Chronic insomnia is a difficulty in falling or staying asleep but is not classified as a parasomnia itself. Periodic limb movement disorder involves involuntary movements of the limbs during sleep but is considered a type of sleep movement disorder rather than a parasomnia.

Thus, nightmares are the quintessential example of a parasomnia because they manifest as disruptive dream experiences that impact the sleep cycle.