It is often possible to select bedroom air temperature at will, but in bedrooms with the window closed for energy conservation and the internal door closed for privacy, the effective ventilation rate is often so poor that CO2 levels routinely exceed 2,500 ppm. This occurs in cold or temperate regions and certainly also in air-conditioned bedrooms in hot-humid regions. This field experiment was the first to examine how bedroom air quality affects sleep and next-day performance. It was shown that both can be significantly improved by increasing the clean outdoor air supply rate in bedrooms. In cold and temperate regions, this could be achieved at low energy cost and with no loss of privacy by installing outdoor air inlets with counter-flow heat exchange in each bedroom, the air exchange being controlled by the CO2 level in the exhaust flow. However, it should be remembered that in some areas noise attenuation and pollution removal technology might then become necessary and that in such areas, the simpler solution of opening a window might have a negative effect on sleep.
Read an interesting article by P. Strøm-Tejsen, D. Zukowska, P. Wargocki, and D. P. Wyon published in the Journal of INDOOR AIR, doi:10.1111/ina.12254. The article reports two field intervention experiments on how the effective ventilation rate in bedrooms affects sleep and next day performance.
The effects of bedroom air quality on sleep and next-day performance (link here).