Cartoon Gravity

You watched too many episodes of Looney Tunes (or some medieval equivalent on stage) as a child and was blessed with the unfathomable powers of Wile E. Coyote.

If you walk or run off an edge in which there is an altitude change above 5 ft, roll a wisdom saving throw. If you roll lower than your passive perception, you do not notice you have nothing to walk on but you continue walking anyway. Continue making wisdom saving throws at the beginning of each turn and should you pass, you notice you are floating. You can use your Reaction before you begin to plummet to your death. Normal fall damage rules apply.

If anyone tried distracting you with the intention to snap you put of your cartoonish trance, roll with with disadvantage. (but pick the highest value as if rolling with advantage)

This does not apply when travelling up or down stairs or where there is direct intent on changing altitude. Discuss with the DM when these rules are appropriate.