Duplicated page overwriting original

Folks, this has been an unmitigated disaster, I am teaching on Tuesday and spent all day preparing the material. I then duplicated the page and deleted half the content from the duplicate only for it to disappear from the original page too. Is there anything you can do? I do not have time to recreate everything!!!! I am so frustrated and annoyed right now, the new Express is massively inferior to the old one.