A 45-year-old male with chronic pain syndrome and opioid use disorder maintained on methadone 80 mg daily presents with worsening fatigue, morning headaches, and difficulty concentrating over the past 6 months. His psychiatrist notes cognitive slowing and depressive symptoms. A polysomnography is ordered and reveals an apnea-hypopnea index (AHI) of 32 events per hour. The study shows predominantly apneic events characterized by cessation of airflow lasting 10-40 seconds with concurrent absence of respiratory effort on thoracoabdominal strain gauge monitoring. There is no evidence of upper airway obstruction, and the events do not demonstrate the crescendo-decrescendo pattern of airflow. His BMI is 24, neck circumference is 15 inches, and Mallampati score is class I. Which of the following is the most likely diagnosis?