Why do our legs and feet go to sleep after sitting for long periods?

Answer 1

When you sit in one position for too long, you are compressing blood vessels that supply an area. When you sit on your butt, you compress the vessels that supply your feet and legs. The tingling you feel is called parasthesia and is a response of your nerves to the decreased blood flow.

Answer 2

the pressure almost seals off a blood vessel depriving the area of blood and oxygen which is brought back to the brain telling it there is a block that is stopping blood flow and the brain then tells you that you should adjust so you can get blood down there is is clearly a defensive mechanism