Rising atmospheric CO2 is a very real concern, and I am very concerned about the long-term mental effects of atmospheric CO2 rising into the 900+ range. But sh

Rising atmospheric CO2 is a very real concern, and I am very concerned about the long-term mental effects of atmospheric CO2 rising into the 900+ range. But short-term, the effects of any rise from 350 to 400ppm outdoors is going to be vastly dwarfed by indoor factors (in some poorly ventilated buildings like old schools, PPM can rise to 2000+). It's far more likely that what you encountered was due to poor ventilation than due to overall global CO2 rise.