gravity - Is there really no difference between up and down in ISS?

I can think of one place where you would prefer to have your head in a specific direction.

The nadir (Earth facing, or "down") Cupola module is a popular place among the cosmonauts, where you can look down at the Earth. Here, you want to stand in such a way that your head is able to watch out of the windows.

Beds do not have a preferred direction, in fact, the sleeping compartments are stacked in a square around the node-2 module in the American segment.