I have sleep apnea and use a C-Pap with oxygen also What can too much oxygen cause?
Oxygen makes you more alert and clear thinking. Navy pilots are
required at times to go an 100% oxygen prior to an approach if
cruising altitude has been higher than a certain level
If, however, you are a carbon dioxide retainer, excessive oxygen
can be fatal. In a CO2 retainer, excessive O2 can cause the
respiratory system to slow, and cause a fatal amount of CO2 to
build up in the lungs. I have personal experience with this, and
nearly over dosed on O2 on one occasion.