My response to her was as follows:
On a positive front, masks can potentially improve your mental state by lifting the carbon dioxide (CO2) levels that you’re inhaling which then results in the release of more oxygen (O2).
The challenge is that when your baseline (normal) breathing is dysfunctional, your tolerance for CO2 will likely be low, which means your brain and body will not be used to the higher levels of CO2 which you will be inhaling as a result of wearing a mask.
In fact, the respiratory center in your brain may think that you are starving for air and you may feel a rise in anxiety or even panic. Usually the consequence is hyperventilation or over-breathing which makes things worse. Unfortunately as a result of the Bohr Effect, 1 & 2 the bioavailability of O2 is reduced when breathing faster and bigger volumes of air than we need.
The only way to properly combat this is to retrain your breathing – start getting used to more CO2 – unfortunately there isn’t a quick fix.