Final answer:
The most common symptom of narcolepsy is sleep attacks, where individuals fall asleep uncontrollably during waking hours. While other symptoms like cataplexy and hypnagogic hallucinations occur, they are not as prevalent as sleep attacks.
Step-by-step explanation:
The most common symptom seen in patients with narcolepsy is D. Sleep attacks. These are instances where the individual cannot resist falling asleep, even at inappropriate or potentially dangerous times. Symptoms of narcolepsy can vary widely among sufferers, and effective treatment often involves a combination of stimulants and other medications. Cataplexy, characterized by a sudden loss of muscle tone often triggered by strong emotions, is another common symptom, but not as universally present as sleep attacks. During narcoleptic episodes, some patients may experience hypnagogic or hypnopompic hallucinations, which are vivid, dream-like hallucinations that occur while falling asleep or upon waking, respectively. However, they are not as typical as sleep attacks. The treatment for narcolepsy often includes psychomotor stimulant drugs to combat the excessive daytime sleepiness and other interventions targeting different symptoms.