Ok, is the headache caused by too much continuous flow oxygen through the sinus cavities, or from the back up of CO2 due to shallow breathing. I have experienced both.
When the headaches woke me last night, I sat up and took slow deep breaths. Exhaling to the bottom of my lungs, and inhaling to top.
I would be surprised if anyone other than medical/respiratory people know this (I only learned about this 3 years ago), but the gas exchange takes place in the lower third of the lungs. Unfortunately, due to gravity, the worse congestion tends to build up in the same place. When I learned how to push beyond a normal breath and get the bottoms of my lungs cleared, I was able to keep the CO2 problem at a minimum. Not only will excess CO2 cause headaches, but being toxic, will cause other problems. You must get air movement in the bottom of the lungs to expel the CO2.
When I suggested to the medical professionals that the O2 was the culprit, they all disagreed, but last night was all the proof I needed. After 5 to 10 minutes of the deep breathing, without the O2, the headache cleared up. As soon as I re-introduced the O2, the headache came back almost instantly. After 4:00 am, I decided to try the rest of the night without the O2. Even with shallow breathing, the headaches did not return. Even when my breathing became shallow, there was not any sign of the CO2 backup, and no headaches. The only problem was being awakened frequently to take deep breaths to pull in more oxygen from the room air.
As I did so, I was aware of just how deeply I was able to breathe, with greater ease than I have experienced in many months (maybe a year or more). Sitting up or lying down, I was able to easily breathe to the bottom of lungs and inhale to the top, and get enough O2 from room air. As my breathing improves, my sleep should follow. Tonight I will try getting through the entire night on room air.
This is definitely great news!!!