I am pretty sure that the chorus is "Millions of balloons tethered to the ground" instead of "heading to the ground". It also makes more sense with the next line considering that the weight of the world is holding them down. Again when considering the line "Cut the strings and let me go" tethered makes more sense. Billions is also swapped with Millions depending on the version of the song you are listening to.
I am pretty sure that the chorus is "Millions of balloons tethered to the ground" instead of "heading to the ground". It also makes more sense with the next line considering that the weight of the world is holding them down. Again when considering the line "Cut the strings and let me go" tethered makes more sense. Billions is also swapped with Millions depending on the version of the song you are listening to.