/characterconfig
UI Settings
HUD

Enable: Display flying text.
Disable: Display pop-up text.

Flying text is your own outgoing numbers, incoming numbers affecting you, and buffs/debuffs enacted by you or affecting you. It "flies" up (affecting your target) or down (affecting you) and fades.

Pop-up text is everyone else's numbers and effects, and they "pop up" and then land with a bounce before disappearing.

Do note that all DoTs enacted by you on a target will tick simultaneously and appear as a single pop-up text event every three seconds. If you have pop-up text disabled, you won't see the tick damage.