I went on cpap last Sept. I had mild sleep apnea with not so mild headaches. Then in Nov, I was placed on o2 for exercise and other activities, like vacuuming, etc. My headaches continued and my pulm doc added 1lpm o2 thru the cpap about a month ago. Headaches are worse. Dr did not want me going over 93% on the o2, but sometimes I see 97 and 98 when I check. No improvement in headache, actually worse. Is it possible to overdose on oxygen? I had the ABG and am not a co2 retainer.