In a dream, a person on average exhales - 10 liters of CO2 per hour. Let`s suppose that we have a sealed room of 20 square meters (50 cubic meters). The concentration of CO2 in the air should not exceed 0.1% (in nature - 0.04%).
A caring mother has well ventilated the room before bedtime, with a CO2 concentration of 0.04%. In 8 hours of sleep a person will exhale 0.08 cubic meters of CO2, which is 0.16%, by morning the concentration of carbon dioxide in the room will be 0.2% (0.16% + 0.04%), which exceeds the permissible value of 2 times.
In the active state the person exhales on the average 30 l/hour (small, domestic activity). 20 m2 (50 m3) of airtight room volume will add one hour of breath to CO2 concentration 0.06%. In total, the initial concentration (0.04%+0.06%) is 0.1%, which is already equal to the upper limit of CO2 concentration in the air. Accordingly, for healthy breathing it is necessary to ventilate the room every hour when awake and every 3 hours when sleeping.