I'm 125 pages into my book and now the Word program that it's being written on opens with the message that the document is repaginating. What does this mean? Should I be worried that I'm going to lose it?

I've only ever used Word before for simple tasks. I tried looking up instructions on what this meant and how to fix it, but I'm too unfamiliar with the program to follow the directions. I don't seem to have the options they list anyway.

Help, Help, Help. Should I open a new document and continue my story in that? I've been saving copies in my email account. Will those be corrupted too? Am I corrupted already?