The reason your spool was bouncing up and down is that it was a cross wound spool. They prefer to have the thread come off the top (like a serger cone) than to wind off with the spool. While weighting the spool helps, it can introduce some tension gremlins.
This is a video from Superior threads about the thread types and how they should be delivered.
https://www.youtube.com/watch?v=I1jq...01QRL-QPUNrCbg
They refer to "spools and cones" but you can get spools that are stack wound or cross wound, just not from them. They only sell stack wound on spools.