Do you not have a backup copy of the drawing?
Are you running a PDM or some form of revision system?
Tell you the truth: you totally screwed
as Kevin & Ned mentioned, without PDM, it's sad news, but you will start it over again. The recover/backup might, but less likely, get it back to you
If the drawing is located on a server perhaps check with IT if there's a possibility to restore a back-up.
Locate the file in Windows explorer - click Properties - Previous versions. Sometimes Windows stores an old version here - I dont know when.
Odds are not good, but you might be lucky. I have been lucky maybe one out of three times.
Disclaimer: I am not running an English version of Windows, so I am guessing the terms.
Thomas has good advice. Also:
If the file is located on a server that is backed up frequently, then contact your IT department (if you can) and ask them for a previous version.