I have mixed sleep apnea, Central and obstructive. Have been on cpap for 2 years and it has helped alot. Recently though I awake feeling as though I am Breathing in smoke. I have even gotten up to check, and even woke up My wife to see if she noticed, and its just me . the origional sleep study showed oxegen levels dropped into the 60's is this a symptom of something else or part of the sleep apnea? Also on occasion will experiece shortness of breath just sitting resting.