Not surprisingly, the same study coincidentally says that prolonged use of masks only causes tiredness and headaches, which coincide with the symptoms of CO2 poisoning, but they illustrate it as minor symptoms.
And even more serious, to maintain that the feeling of suffocation is psychological, that is a fallacy. In addition, these statement is not part of the scope measured in the study. But then again the scientific method here was absent.
What they did here is called “study design”; there is people tied to pharmaceutical industry (handsomely paid btw) to design the studies in a way that the results will favor their interests.