Underrated rationality hack: Buy a CO2 sensor, and open the window when it alerts. Best 70 bucks I spent in a long, long time.

Why? Because CO2 levels that are routinely exceeded indoors nowadays can inherently have incredibly detrimental effects on rational thinking, and CO2 levels rising are also often indicators that other air quality aspects that affect rational thinking are going down and that ventilation would likely help you think by targeting multiple problems at once. In many places this is getting worse, not better, as modern houses are more hermetically sealed for insulation to save energy, and work spaces and homes become more crowded, while outdoor CO2 is rising planet-wide, people move to cities with ever less green as the housing crisis is tackled, and people have to spend more time indoors against fierce winters and intolerable summers due to climate change (which is very worrying, because now is when we need to be most rational.)

The intensity of the effect on your cognition, how early it becomes noticeable and which functions become noticeably compromised varies a lot with the individual, but the effect can be very pronounced, reducing executive functioning, complex reasoning, speed of thought, mood, sleep https://www.o2sleep.info/Researce_CO2_nextday_performance.pdf , social functioning, motor performance https://www.sciencedirect.com/science/article/pii/S0160412018312807  and overall productivity, leaving you fatigued. While we can observe physiological changes in the brain, it is not yet clear why the resulting functional loss is not evenly distributed in the population - some seem much more resilient, some much more sensitive; you probably won't know which group you are in until you check. Here is a meta-review of 37 studies (it is on sci-hub if your research institution does not have access) to mostly illustrate that this is a common enough issue to warrant checking for you individually and ensuring in your office spaces: https://onlinelibrary.wiley.com/doi/abs/10.1111/ina.12706 

Humans evolved in CO2 levels of 200-280 parts per million. Our outdoors meanwhile averages 420 in summer due to all the fossil fuels we burned, but can easily breach 500 in cities in the Northern hemisphere in winter. Forest and ocean carbon capture loss will worsen this. Being indoors amplifies this a lot. In a small room without ventilation, even if you aren't doing much of anything beyond existing, you will raise levels by around 100 an hour; much more if you exercise, or burn gas, or aren't alone. It is not rare for indoor levels to reach 2500. By 1000, humans typically start losing the ability for complex reasoning.

For me, high CO2 manifests as being headachy, irritated, brain foggy, difficulties mustering willpower, slowed thinking, trouble focussing, trouble being patient, trouble getting restful sleep, with effects becoming noticeable over 750 already, and debilitating at 1100. But it manifests differently in different people - this might not hit you as hard, but in that case, gift the sensor to your office to ensure average productivity there; a bunch of people there will be hit this hard by it.

If you are affected, you will notice the effect, but the cause is undetectable to you. You can't smell or see CO2. And there are many other plausible causes, so just feeling unfocussed does not tell you want went wrong and how to fix it. If you are in a long-running meeting in a small room, there are many reasons to become frustrated and unfocussed; if you step into a forest, there are many reasons to become focussed. You won't know if opening the window is a solution, and set yourself up for a mere placebo effect. But with a sensor, you get a connection. You are annoyed you can't focus, it chirps, you go fuck, this air quality went down the drain, open the window, breathe for a few minutes... and feel clear headed again. The correlation is eerie. 

Anyhow. You can buy CO2 sensors in various places online and offline; I hate to admit I got mine from amazon. You want one ideally set to depict current levels, as a specific number; you can also have colour codes and even alarms if very high levels are breached. I am happy with the one I got https://www.amazon.de/-/en/gp/product/B093L47XZ9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1  - a small one that is usually plugged in, but can also run on the battery for a day and be portable, which allowed me to check out places like my office too, and make changes. It warns you acutely, and allows you to instantly fix the issue by opening a window, and it shows you trends so that if a problem recurs and needs a systematic fix, you can e.g. debug your ventilation system or ventilation habits. Just make sure to regularly recalibrate it outside (that will itself get trickier as this crisis worsens, as we will lack a reliable low source to recalibrate, but for now, seems generally unavoidable in affordable models, and for now, still works.). It has significantly improved my quality of life, and I just wanted to share.

Also - another reason to target fossil fuel emissions now. The emissions are making us, quite literally, stupid. The idea of stepping into my garden, and still not thinking clearly, because we have poisoned the air of our entire planet, is horrific to me. There is genuine concern the air alone will end up making us sick, and that independent of the far more pressing resulting collapse of the climate, we need to fix this for this reason alone: https://www.nature.com/articles/s41893-019-0323-1 

Final interesting side note: The fact that effective ventilation systems often require us to use energy to actively pull air through small tubes, and that this air being sucked out of buildings is very enriched with CO2, comes with a potential interesting side application: installing a carbon capture device inside your green powered ventilation system, thereby becoming net carbon negative. https://www.sciencedirect.com/science/article/abs/pii/S0048969722061873