Widgets appearing beneath posts

I recently added some basic widgets to my blog, which uses Desk Mess as a theme. When first added, the widgets appeared where they were supposed to, in the right hand sidebar. This remained the case for a week or so.

Today, for no explicable reason that I can determine, all the widgets appear below the postings. The right hand sidebar is empty. I have tried removing the widgets and re-entering them. I have gone into theme editor to see if there was anything I could find and change, but nothing seems to match the problem.

Is this a glitch in Desk Mess or WordPress? Or is it something I did inadvertently? Has anyone else had this happen and can offer a solution?

Thanks very much.