Of course, these CO2 levels are smaller by at least one order of magnitude than what could cause suffocation. I overdramatized the fact that the air quality was really, really bad.

Based on every article I found, above 1000 ppm clearly affects sleep quality, cognitive performance, it causes headaches, etc. so 3600ppm is generally considered really bad.

Even if CO2 would be harmless in itself, it is a good indicator for bad ventillation.