Patient presents with symptoms suggestive of nocturnal hypoxemia, including daytime sleepiness, morning headaches, and impaired cognitive function.  The patient reports snoring and witnessed apneas observed by a bed partner.  Physical examination reveals obesity with a neck circumference of 43 cm and mild hypertension.  Polysomnography was conducted and confirmed the diagnosis of nocturnal hypoxemia, demonstrating recurrent episodes of oxygen desaturation during sleep, with a mean oxygen saturation of 88% and an oxygen saturation nadir of 78%.  The apnea-hypopnea index (AHI) was calculated at 25 events per hour, consistent with moderate obstructive sleep apnea.  Differential diagnoses considered included central sleep apnea, obesity hypoventilation syndrome, and heart failure.  However, the polysomnography findings, along with the patient's clinical presentation, strongly support the diagnosis of nocturnal hypoxemia secondary to obstructive sleep apnea.  Treatment plan includes weight loss counseling, continuous positive airway pressure (CPAP) therapy initiation, and follow-up polysomnography to assess treatment efficacy.  ICD-10 code G47.33 (Obstructive sleep apnea syndrome with excessive daytime sleepiness) is documented.  Patient education provided on the importance of CPAP adherence and lifestyle modifications for managing sleep apnea and its associated nocturnal hypoxemia.  Referral to a sleep specialist is made for ongoing management and optimization of CPAP therapy.  The patient's prognosis is good with adherence to the recommended treatment plan and lifestyle changes.