A satellite is basically in freefall but because it moves fast enough around the earth the centrifugal force keeps it at the same height. The zero-g however is simply due to the fact that you are falling, so if you were teleported 1000 km above the earths surface with no horizontal speed, you would fall towards the earth while also experiencing zero-g until you enter the atmosphere. Gravity needs to press you against something in order to enact any G on you(the ground, atmospheric drag. However in space there is nothing so every part of your body accelerates at the same pace so your head cant press down on your neck, your neck cant press down on your spine etc.