Have you considered the effects of low barometric pressure/low oxygen levels. You can measure this with a barometer and oximeter. If the pressure drops on the barometer, oxygen levels in the air should diminish slightly. You may be sensitive to this adjustment. Check your sensitivity by comparing a normal reading on an oximeter to the current reading when the barometer falls. If your oxygen levels in your blood drop, you may need to supplement your oxygen levels with an oxygen concentrator.