Sleep Physiology and EEG

A 38-year-old male software engineer presents to the sleep clinic with a 6-month history of excessive daytime sleepiness and sudden episodes of muscle weakness triggered by laughter or emotional stress. His wife reports that he frequently jerks his limbs during sleep and sometimes stops breathing for 10–15 seconds. Polysomnography shows an AHI of 18/hour, and MSLT reveals a mean sleep latency of 6 minutes with sleep-onset REM periods in 3 of 5 naps. What is the most likely diagnosis?

A 52-year-old woman with a 10-year history of progressive insomnia and cognitive decline is referred for polysomnography. She reports vivid, distressing dreams and frequent nighttime awakenings. Her daughter mentions that the patient sometimes acts out her dreams—thrashing in bed and shouting—despite appearing asleep. PSG shows increased muscle tone during REM sleep with prominent phasic EMG activity in the chin and legs. EEG during these episodes shows a low-amplitude, mixed-frequency pattern typical of REM sleep. What is the most likely diagnosis?

Which EEG frequency band is characteristic of the awake, alert state with eyes open?