The issue is working from it in a email, this you should never do, but first save it to your computer then edit it.
You may or may not be able to recover this document since the changes are saved in your Temporary Internet Files folder. Note that you can't just open your Temporary Internet Files folder directly and find it due to the way Windows handles your Temporary Internet files but if it's still available, here's how you can get it back:
Open another Word document sent to you as an attachment from an email. If you don't have one, send an email with an attachment to yourself. (While you should be able to open the same email attachement since another copy of the file is created in your Temporary Internet Files folder)
Then click on File, Prepare, and then click Properties. The Properties pane will display below the Ribbon.
On the far right of the Properties pane you'll see a file path and the document name. Select only the file path and press Ctrl + C to copy it.
Press the WinKey + E to open the Windows Explorer. (Or use an alternate method to open it)
Paste the copied file path in the Address bar and press Enter.
These steps should put you either in the same location as your revised file or near it. You may need to dig around in other folders to locate it.
Let me know how you go please