I was just diagnosed w/sleep apnea & was told my oxygen dropped to 68. I know normal levels are in the 90s. What is the effect of levels in the 60s?

Sleep apnea. This is a serious condition. Low levels mean that your system esp. Your brain is suffering from periodic deprivation of normal oxidation of the blood, which is dangerous, you should be under care for the apnea, which often is applying pressured air via a face mask to keep oxygen levels normal.
Many. Hypoxia into the 60s is quite serious. Risks include, but are not limited to, hypertension, heart failure, stroke, heart attack, and even death.