Blood goes down to your feet all the time, but the muscles movement prevents it from just sitting around in your feet. During a flight, because you sit around for many hours, the blood just stays in your feet, resulting in there swelling up.
Gravity.
No; chlamydia will notcause your legs and feet to swell.
Pregnancy may cause your feet to swell.
if they are on your feet: it could happen if they are not on your feet: no
Your feet swell
the atoms inside your feet get bigger in heat
Yes
yes
Because of all of the pressure that you put into it
Malnutrition would affect your whole body, not just your feet.
Increased blood flow which congregates at the lowest part of the body (the feet).
36,000 feet
it is 5000 feet long