Quilting Headache - thread trouble

I am working on a holiday quilt to sell, and hit on a nasty issue. My thread suddenly began to drop down under the material. It was all loose, so that the loops for the top thread were on the bottom of the quilt, with the bobbin thread just sort of channeling through them without being tucked back up into the material.

Turned out after I tore the thread out and redid it three times, that I had moved the feed spool, which made the thread on the top flow more smoothly than it had before, so my tension needed to be tightened up on the top thread. Drove me nearly to tears before I remembered I had moved the feed spool, then it was simple to sort out why halfway through the quilting my machine no longer worked right for quilting that material.