[hgsgm]

When you aren't moving you feel pressure due to you and the planet trying to free fall into each other to make a black hole, or at least pass each other in very close orbit, but being blocked by the repulsion of your electrons vs your shoes'/floor's/ground's.

When you are falling, you are feeling the air that is hitting you because it is not falling, causing the electron effect above, and your guts feel weird because your brain is noticing that nothing is pushing on them anymore.