Which of the following is a characteristic feature of narcolepsy?

Narcolepsy is a neurological disorder characterized by excessive daytime sleepiness and sudden episodes of muscle weakness, known as cataplexy. The presence of cataplexy is a defining feature of narcolepsy and can occur during emotional situations like laughter or surprise, causing a temporary loss of muscle tone. This characteristic helps differentiate narcolepsy from other sleep disorders.

Excessive daytime sleepiness can manifest as an overwhelming urge to sleep during the day, often without any preceding tiredness. This symptom can severely impact daily functioning and quality of life. Therefore, the combination of pronounced daytime sleepiness accompanied by episodes of sudden muscle weakness uniquely identifies narcolepsy among sleep disorders.

In contrast, other conditions listed, such as increased sleep duration, sleepwalking, and chronic insomnia, do not align with the hallmark features of narcolepsy. Increased sleep duration could indicate other sleep disorders but does not specifically relate to the sudden muscle weakness seen in narcolepsy. Sleepwalking is more associated with non-REM sleep disorders and is not a feature of narcolepsy. Chronic insomnia involves difficulty falling or staying asleep, which contrasts with the daytime sleepiness experienced in narcolepsy.