No, your image sensor isn’t really upside down, but the image projected onto it is. This isn’t really important for the act of taking a photo, because the camera flips the image for you. It IS important, however, when you clean your sensor. Keeping this fact in mind can save you a few swabs (and a few bucks).
After swabbing a sensor, it’s a good idea to take a test shot and check for dirt left behind. I don’t know about the rest of you, but I rarely get it all on the first try. I usually end up with a few spots on the top or the bottom of the image. When I go back for round two, I have to decide which end to pay more attention to, because the swabs don’t have a perfect reach across the entire height of the sensor. Knowing that the image is projected upside-down onto the sensor , I know that if I have spots on the top of the image I need to swab toward the bottom of the sensor.
It works, and it’ll save a few swabs.