What would cause unity to reset all scenes in a project?

I was working on a project, simple roller-ball game for a friend. simple three levels, all of that. I had it working, i built it, and now I’m going back through the project in unity and for some reason everything has disappeared. The scenes were set back several days worth of work.

This same thing has happened to me and I have no idea why. I think all my assets were there, but my scenes were reset.

I just simply make a backup of my project after I’ve done quite a bit of work.