you may want to add another wrinkle to trappers suggestions. you can add an ounce of H2O2 (Hydrogen-Peroxid) to a humidifier and then leave that running in the same room as you sleep in all night. the oxygen gets diffused into the air and will be absorbed by your lungs. a great way for anybody to increase oxygen content of the air. i plan to do this this winter when it gets too cold to leave the windows open.