> The words “up” and “down” are absolute, but the words “left” and “right” are relative to you.

I disagree. In this sort of conversation, "up" refers to the direction from your feet to your head, not away from the ground. If you do a handstand and hold your piece of paper up to the mirror then you'll still find it flipped left-to-right but not top-to-bottom if you turn it the instinctive way, and still find it flipped top-to-bottom but not left-to-right if you turn it vertically.