Note that if you were to lie horizontally, on your side, on a couch, and
view your image in a door mirror, with your arms extended vertically, there
would be an UP/Down reversal of your image’s vertically spaced R/L arms.
Ie., if your right arm is extended upward, your image’s right arm would be
extended downward. Your horizontally spaced head and feet would not be
reversed. The essential concern is in the completly different meanings we
imply by the UP/DOWN vs the LEFT/RIGHT distinctions.