I recently cleaned my home's air filters and discovered a significant increase in well-being. Previously, staying at home during the weekend for more than 1-2 hours resulted in fatigue and dizziness, whereas being outside or at work during the weekdays (indoor environment with commercial/industrial-grade HVAC) did not.
My carbon monoxide detector couldn't find anything so CO was not likely the cause of the problem. Conditions also improved when the heating was turned off.
After the cleaning of air filters (edit: there was a lot of unknown black material stuck in the filters during the clean), no such fatigue nor dizziness occurred, even with heating turned on.
So based on this experience, I suspect the difference has something to do with the concentration of leaked natural gas compared to air flowing through the filters into the house.
Is there a recommended method and tool to detect natural gas, or any more accurate cause of the problem, so that I can better detect and prove such a phenomenom (something causing unusual fatigue and dizziness over time) in any given location, especially when changing air filters myself is not an option?