Hey all,   As some might be aware a few years back I built a garden office/shed, insulated well and sealed it up as best as I could. Recently, when working in the office I had started to noticed feeling drowsey or 'foggy', sometimes headaches and certainly always in the afternoon (and this is without going to the pub for lunch!!)   Anyway, I purchased a Netatmo weather station with indoor Co2 PPM monitor (was on offer), only turned it on this morning but already it's showing