Under 90 Blood Oxygen During Sleep: Causes and Management Blood oxygen levels are an important indicator of respiratory and cardiovascular health. A healthy level of blood oxygen saturation should range from 95-100%. However, during sleep, it is common for the levels to fluctuate slightly. If the levels drop consistently below 90%, it can lead to serious complications. There are various reasons why someone might have under 90 blood oxygen levels during sleep. Some of these include sleep apnea, chronic obstructive pulmonary disease (COPD), lung disease, heart disease, obesity, or hypoventilation syndrome. Certain medications, such as opioids or sedatives, can also cause a drop in blood oxygen levels during sleep. Sleep apnea is a common cause of low blood oxygen levels during sleep. It occurs when the airway becomes blocked, leading to pauses in breathing. This can cause drops in blood oxygen levels, which can lead to serious complications such as high blood pressure, heart disease, and