Answer:
You get some type of pressure that you start to feel in your muscles and joints from gravity and movement. How do they say it? Something called "seat-of-the-pants" (something like that). You get some type of pressure, and your body senses it, and it knows when you are upside-down or not, because if you're not, then you won't get any pressure in your muscle.
Hope this helped!
Have a supercalifragilisticexpialidocious day!
