Hi Starlight,
I would think it is gravity. The feet and hands do the most work daily. When they rest, the blood is accumulated there.
I think gravity is the reason people are pear shaped, the reason people get vericose veins and the reason your face or whole body hangs.
This shows up on inactive people. Active people and people who take care of themselves, like using a mud mask, eating right etc. can delay the effects of aging.
I'm no authority, but I have an Inversion Table. It is one of the best investments I've made.