Why do I immediately get sleepy when the airplane closes its doors and pressurizes the cabin?

[kayaker]

I’ve always blamed the three Bloody Marys and the brownie.

[Hail_Ants]

@Pasta

This is immediately refutable from other evidence. If the pressured dropped that much, your ears would pop and your half-filled water bottle would crackle (and, if opened, would hiss). None of that happens.

There is also no mechanism present to reduce the pressure in the cabin lower than ambient. Compressed air is used to keep the interior pressure above ambient when flying, but there’s not a big vacuum unit or anything to reduce the pressure below ambient.

Yes. Plus if the pressure outside was ever significantly greater than the pressure inside the plane I don’t think the fuselage would even maintain structural integrity (i.e. it would implode like pouring water on the hot, sealed can trick). A difference in relative altitudes like that would represent tons of pounds of pressure pushing on the outside of the aircraft. Aircraft are designed exactly the opposite of this (shaped like a pressure flask, self-sealing ‘plug’ doors etc.)

Also, if the pressure dropped suddenly like that it wouldn’t just make you drowsy, it could give you the freakin’ bends!

[Ethilrist]

@Alessan

If you usually sleep on flights, it could be a simple Pavlovian response.

When I was in college, we had a guy who worked in the music building who used to tour as a trumpet player with Duke Ellington. He played with the pep band, and when we went on our annual road trip tour up to Humboldt State, he’d get on the bus and fall asleep. Didn’t matter what time of day it was; for him, bus = sleep.