Directory has disappeared from hard drive

Search for the directory name in explorer. Maybe you moved it to a another directory by accident.

Right-click the parent folder and select properties. Go to the "previous versions" tab. You may be able to recover the sub-folder by restoring it's parent to a previous date. This is assuming you have system restore enabled for that drive.

I had directories disappearing twice. Both times it turned out to be my copy tool, TeraCopy that had made a 'Fast Move'.
I did not deliberately do any moves so something buggy.. Thing is that Windows search did not show the directories or the files. They were not hidden and obviously not in recycle bin. They showed with original location in registry. Just by accident i happened to find the log for TeraCopy and after that i found the missing folders by manual search.
BUT like i said, windows couldnt find them when i searched by directory name, file extensions, whatever.. does the search only
read the Registry? that would explain it. SO, try searching manually..Good luck