The normal sleeping oxygen saturation level is above 90 percent, according to Central California Ear Nose & Throat Medical Group. When oxygen levels drop below this, oxygen desaturation occurs. This is often caused by decreased breathing.
Obstructive sleep apnea, or OSA, is a common cause of oxygen desaturation, states CCENT. No specific cause is known, but many factors appear to contribute to a blockage of the airway. These including a long palate, large tonsils, and a large or high-riding tongue. The tongues of people with receding chins are often located further back in the throat, as well. Obesity sometimes aggravates the condition.