Which condition is characterized by excessive sleepiness during the day?

Narcolepsy is a neurological disorder that affects the brain's ability to regulate sleep-wake cycles, leading to excessive daytime sleepiness. Individuals with narcolepsy often experience sudden and uncontrollable episodes of sleep, known as "sleep attacks," which can occur at inappropriate times, such as during conversations or while working. This excessive sleepiness is a hallmark symptom and can significantly impact daily functioning and quality of life.

In contrast, insomnia primarily involves difficulties in falling asleep or staying asleep, leading to poor sleep quality, but it does not inherently cause excessive sleepiness during the day. Sleep deprivation results from a lack of adequate sleep, which can also lead to daytime sleepiness, but it is not a condition characterized by sudden sleep attacks. Restless legs syndrome is a condition that causes uncomfortable sensations in the legs and an uncontrollable urge to move them, particularly during periods of rest or inactivity, which can disrupt sleep but is not directly associated with excessive daytime sleepiness.