Madonna might have “Back[ed] That Up to the Beat” a little to hard — as she ended up on the floor during a recent stop on The Celebration Tour. On Sunday, February 18, the Queen of Pop fell off of her chair in the middle of a performance at Climate Pledge Arena in Seattle, Wash. In several viral videos shared to social media after the accidental tumble, Madonna and one of her backup dancers could be seen attempting to perform a choreographed dance routine in which the “Material Girl” singer is dragged backward while seated in a chair on stage. Madonna was singing her hit song “Open Your Heart,…