A family of Microsoft word processing software products for creating web, email, and print documents.
May I start by saying I have no idea what happened to your document, however I was attracted by your comment "plus it was automatically saving".
No version of Word automatically saves the document!
You could use a macro to automatically save, e.g. http://www.gmayor.com/automatically_backup.htm but the only 'autosave' is of recovery information and that only occurs in the event of a crash.
I would also urge you to check the option box to automatically create a backup.
If you display filename extensions (and also hidden files) in Windows Explorer, you may have better indication of what is happening with your filing system, as then it is less difficult to confuse macro enabled formats with macro free formats, and to confuse templates with documents. You can also check for the presence of unwanted lock files - http://www.gmayor.com/what\_to\_do\_when\_word\_crashes.htm
If you used SaveAs to save to another format, the original format document should remain, even if inadvertently you managed to delete text from the document before that save.
Open what remains of your document and click File > Manage Versions to see if there are any other versions of your document recorded.