Oy! Sorry to hear that!
When I am writing in Evernote (I also use it that way), I pretty much manually sync it every time I pause writing. I’m not sure, however, whether that would have helped here, or whether what Norton was doing would have interfered with that. In any case, it’s a sober reminder that I probably shouldn’t be using it to write and should be using an offline processor or simply paper.
Hopefully you can remember enough of what you were working on that it can be recycled into new works. Sometimes serendipity like that can work out well enough in the end.