I Have Sleep Apnea And COPD And Am Overweight By

I have sleep apnea and COPD and am overweight by about 100 pounds. I use a regular CPAP and all is going well. The last 2 nights I slept longer than normal - six and a half hours. Both mornings I had lower than usual oxygen saturation (by pulse oximeter). Readings about 93,94,95. I am usually at 97 or 98 while awake. Is this due to longer sleep? Is the COPD maybe getting worse? The pulse oxy gets back to normal after about 3 hours awake. How low is too low for oxygen saturation. I am a 67 year old white male.