A 25-year-old woman presents with a 2-year history of excessive daytime sleepiness. She states that she often dozes off at work and feels an overwhelming urge to sleep. She also describes vivid hallucinations when she is falling asleep and has had occasional episodes where she wakes up but is unable to move. She denies muscle weakness triggered by emotions. Polysomnography reveals a decreased sleep latency and rapid onset of REM sleep. What is the most appropriate next step in confirming the diagnosis?
