I was working along with my form, and opened a preview to see how it was looking, and when I closed the preview lightbox, the element list was empty!
I was very confused... All the fields are still in the form when I preview it, but the element list was just not showing them. Then I just happened to click in the white space just before the form name in the element list.
There they were! Seems like there should be a carrot there like in front of the elements to know it's collapsed!