This just happened to me as well, was using Evernote on Firefox and it went down the list of all my notes as if I were hitting the arrow key down, but it was actually rapidly deleting the notes one by one. I quickly clicked off and it stopped it but now I'm back two years of notes. Whenever I refresh the browser the notes are still gone and there are none in the trash.
I went to the Evernote app on my computer and all my notes are still there. They will only appear in the browser if I edit them though. I'm worried that if I refresh the app it will delete all my notes. How can I get these back?