Final answer:
Narcolepsy is a sleep disorder that causes extreme daytime sleepiness and sudden episodes of falling asleep, often accompanied by cataplexy and dream-like hallucinations.
Step-by-step explanation:
The disorder characterized by extreme daytime sleepiness and frequent episodes of nodding off is known as narcolepsy. Narcolepsy is a chronic sleep disorder often accompanied by cataplexy, which is a sudden loss of muscle tone, and can include vivid, dream-like hallucinations similar to those experienced during REM sleep. People with this condition have an irresistible urge to sleep, often falling asleep at inopportune times. It is distinguished from sleep apnea, another sleep disorder, where breathing temporarily stops during sleep. Treatment for narcolepsy usually involves medication and lifestyle changes to manage the symptoms.