Help! Lifted sash really fast, now its balance cord is jammed?

If it's like the many older windows with weights and pulleys that I have worked with over the years, there would be just a heavy iron weight attached to the other end of the cord that is attached to the window sash. From what you describe, you can probably use a very stiff wire, like the kind they use for yard signs, and bend it enough to get it up to poke the weight off whatever it is stuck on inside the cavity.