I had an old helmet with a snap strap on the back that your goggles go thru. I was wearing a backpack that has that loop on the top.
While riding in a tuck, the loop on the backpack hooked over the helmet strap, and when I tried to straighten up, my head was stuck looking straight up at the sky, and the chin strap was strangling me.
Didn't crash, but close. Scared the piss out of me.