Ever wonder why you get so sleepy during conference talks? Turns out lots of conference venues aren't well-ventilated, causing CO2 to rise to levels that cause drowsiness (>1000ppm). Data from @keflavich shows this steady rise over the first 50min of a conference session. The organizers at #MW_Link2019 have done a great job since of keeping windows and doors open. Here is an updated, going until noon. Coffee break is obvious at 10:50, and improved ventilation when the session restarted at 11:20.