All Notes Suddenly Disappeared

Using iPhone 5s and at some point today all of my notes in the notes app have gone. I see other posts about this that claim a problem syncing with the mail app or yahoo mail, but I don't sync notes with those apps. At least not intentionally and not before now. Have had this phone for a year (and a 4 before that with the same rough settings) and have never had a problem losing notes before. Is there somewhere they might have gone to? The idea of something just disappearing seems very strange to me.

Secondly I don't use the iCloud for backups, preferring to use iTunes. After my notes disappeared I plugged my phone into my laptop expecting to be able to restore to an old backup. iTunes auto-backedup my now notes-less phone, so I attempted restoring to an old backup, only to find that the only old backups I have are years old, almost certainly from old phones. There must be a way of restoring my phone to a previous backup? Or is it the annoying case that all backups immediately write over the existing files?

I'd appreciate any help, this is incredibly frustrating...

Thanks,

Mike