I lay awake for about half an hour just pondering the very stupid question: what would happen (to you) if gravity reversed itself for one second?
If you’re in a structure, that’s bad news. When thrown upwards and back down by 15 ft. most will become rubble. All trees would be uprooted.
But, supposing you were outside and survive the chaotic re-settling of terre firma. What would be the worst part?
The atmosphere would not only fall up with everything else, but has been pre-pressurized to explode outward were gravity to free it. Here, it’s not only freed, but helped along as well. So we can expect a very rapid pressure drop, even in just a second, along with the chill of adiabatic cooling. But a brief pressure drop, even a large one, is not that big a deal. There is a far greater pressure differential on a moderately deep scuba dive than between 1 atm and vacuum.
What will really hurt is the overpressure when the air comes crashing back down and compressed (and heated). Enough, I would guess, to pop your eardrums and give you one serious hot&dry enema.
So, making no calculations, I predict, were gravity to reverse itself for one second, a fair many people would survive the material mix up at the surface, only to be battered, perhaps killed, by the worst reverse fart imaginable.
It’s survival of the tight sphincters.