Sounds like it just lost the connection to the db for some reason. Until an extraction completes, completely, no file is created. I don't have an answer for the sleep question.
I've tried multiple times without a success. The last time after 3 hours the computer shut down automatically, saying that it was too warm. It was sitting on my desk and I was working as what I do every day.
I think my database is simply too large. Can I break it into several small ones? Would I be able to append them together afterwards?