Answer :

CO2 narcosis. This happens when people are given too much oxygen...this slows down the oxygen driven drive to breathe and we breathe slower... Then CO2 can build up and reach levels that can be toxic...can be lethal as in hypercapnia.
Carbon dioxide narcosis is when carbon dioxide levels are chronically elevated, the respiretory center becomes less sensitive to CO2 as a stimulant of the respiratory drive, and the PaO2 provides the primary stimulus for respirations.