Any ideas for an antigravity generator?

[JustImagineIt]

I am trying to make a thingamabob that allows the player to move horizontally and only horizontally without falling if they trigger it. I attempted to modify the player velocity(player can't walk), set the player to fly(player can move up and down despite), and set a really high levitation value(just no). Has anyone made something like this before? If so, how?