Empty Directory Listing

I’m developing a site that is still fully functioning; however, I went in to edit the style.css file from the Appearance > Editor area, and I’m getting the message:

Oops, no such file exists! Double check the name and try again, merci.

So I disabled all the plugins (I had tried to install two different forum plugins, which are the only problem I can think could’ve triggered the problems, which I deleted). When I went in to FTP to see if I could see the files, the theme folder is simply empty. So the site still works… but the theme folder is completely empty.

I tested it on a different browser to see if it was just caching in Chrome, but it works over there too. I tried turning on a different theme and switching it back and that didn’t work. Does anyone have any pointers? I’m not sure whether to panic or scratch my head.