With my twitchy mouse finger, I accidentally slipped an existing Category "into" another Category with the result that the original became a Sub-category to the second one. I tried right-clicking on the Sub and clicked on Edit and saw in the drop-down menu the choice to have it convert into a Category. But it did nothing. I'd appreciate any help as always. I'm using PSE11.
Probably too late now, but Undo in the lower left corner would probably have worked if you did it right after your mistake.
Why not do the following: 1. Make a new Category with the name you wanted. 2. Assuming you have already assigned pictures to this same Category name but it is residing as a Sub-Category, select them. 3. Now assign them to the new Category you made in Step 1. 4. Once that is done, Delete the misplaced Category that is a Sub-Category. That will delete all of the image assignments to it, but not affect the images themselves.
This should correct your problem.
I tend not to drag/drop when I can avoid it. I have done what you did a few times myself.