What sleep disorder is characterized by pronounced sleepiness during the day due to loss of orexin neurons?

Narcolepsy is a sleep disorder that leads to significant daytime sleepiness and is closely linked to a deficiency of orexin neurons, which play a critical role in regulating wakefulness and arousal. Orexin, also known as hypocretin, is a neurotransmitter that helps maintain alertness and energy levels. When orexin-producing neurons in the hypothalamus are lost or impaired, as seen in narcolepsy, individuals experience uncontrollable episodes of sleep during the day, even in inappropriate situations.

This disorder often includes symptoms such as sudden sleep attacks, cataplexy (a sudden loss of muscle tone triggered by strong emotions), and disrupted nighttime sleep. In contrast, conditions like insomnia involve difficulty falling or staying asleep, sleep apnea is characterized by interrupted breathing during sleep, and restless leg syndrome involves uncomfortable sensations in the legs and an uncontrollable urge to move them, particularly during periods of rest. These other disorders do not directly stem from the loss of orexin neurons, making narcolepsy the only option that aligns with the specified characteristics in the question.