Totally agree. I’ve always assumed that high CO2 levels and low air pressure must have some effect on drowsiness and cognition
Edit: some googling shows that commercial flights can reach 1500 to sometimes 3000 ppm co2. Pressure is around 0.75 atm at cruising altitude. My understanding is that would be noticeable
Confirmed, flown SF-Toronto round trip multiple times, Toronto-SF-South Korea, Toronto-London, and on both narrow body and wide body aircraft I'm lucky to get less than 1800ppm, with peaks at 3100ppm (on the London flight) according to my aranet4 placed either at the top of the magazine pouch or in an open exposed pocket in my bag on the floor.
The study i saw this on was a review of data from 200ish US domestic flights. Maybe you were close to a vent, or some other variable im not thinking of, or just an outlier
Edit: some googling shows that commercial flights can reach 1500 to sometimes 3000 ppm co2. Pressure is around 0.75 atm at cruising altitude. My understanding is that would be noticeable