So, I decided to try freehanding a design, and I used the pencil tool. Then I was working with it.
But somewhere along the line, my curve turned into a beizer guide, which I don't want and will probably never need. Then, by accident, I right-clicked and hit "Make Guides" without realizing it.
It's already been saved and closed, so there's no way I can undo it. How can I turn it back into a path?