for a long time i've wondered why i was so sleepy. i often work out of my apartment (a new building), and NYC being NYC, my windows and doors are often closed to allow for air conditioning.
i bought an awair sensor, and when i plugged it in, i was getting readings of 1000-1500ppm on CO2. immediately started ventilating the apartment, outside weather be damned. impossible to tell, but i feel more awake and healthier in general now. i also make it a point to get outside more and work more from my office (which is very big and airy and lightly attended).