We need CO2 in our bodies.  When I used to have panic attacks, my "go to" remedy to help quickly was to breathe into my hands (out through the mouth and in through the nose) to replace lost CO2 to balance out the O2 and CO2 requirements. 

Quote from article:

" Biologist Dr. Ray Peat tells us that, “Breathing pure oxygen lowers the oxygen content of tissues; breathing rarefied air, or air with carbon dioxide, oxygenates and energizes the tissues; if this seems upside down, it’s because medical physiology has been taught upside down. And respiratory physiology holds the key to the special functions of all the organs, and too many of their basic pathological changes.” "

https://drsircus.com/general/hypocapnia-lowered-co2-in-the-blood-leads-to-reduced-oxygenation/