Post content disappeared, can't find autosave

This is the first time I’m having this kind of problem.
I came back to a draft and the content box is now totally empty – my text has disappeared, even though I clicked ‘save’ before exiting. Past revisions are all empty. In fact it seems that between the moment I created the post and I exited there were no autosaves.

Did I do something wrong? Can I do anything to get my draft back?