Why You Still Feel Tired After Treating Sleep Apnea

Around 30% of people treated for obstructive sleep apnea (OSA) still report significant daytime fatigue, according to new research. This "residual sleepiness" could be due to a blunted cortisol awakening response, and not just fragmented sleep architecture. The finding points to the HPA axis as a key player in why some feel groggy even with good CPAP compliance.