I am not sure that nullifying one's inertia would "reverse gravity". It would mean that you personally would exert no gravitational pull on anything else. That much is certain.
It *might* mean the converse as well -- nothing would exert any gravitational force on YOU. The more I think about it, the more I agree. You would be weightless.
It would mean that you would have no 'resistance' to any force applied to you.
So, a 5 MPH breeze would have a greater force on you than it would on a dandelion! You would immediately drift off at whatever speed the wind was. If you crashed into anything, it would not hurt you at all. You would instantly lose your speed. You would instantly take on whatever speed your environment had.
Then there's the force of sunlight hitting you.
If your inertia was actually absolute zero, then I can think of no reason why -- at the first light of dawn -- you wouldn't be instantly blown off the Earth and propelled away from the Sun at the speed of light. Then again, you would be absorbing EM radiation from all directions, so as you left the vicinity of the Sun, you would be blown away from the nearest stars, then the nearest star clusters, then the center of the galaxy, then the nearest galaxy cluster, until finally....
you would come to rest in the nearest large starless, matterless, dark, lightless, VOID in the inter-galactic web.
