I had the same problem this morning. The note I made last week with the phone numbers for a new client I have to call today suddenly disappeared this morning from my Macbook Pro. I checked all my other Apple devices, and it was not on any of them.
This is using iCloud for the sync, as I do not have a google account to use for this type of stuff.
I managed to get my telephone numbers back by looking in the file ~/Library/Containers/com.apple.Notes/Data/Library/Notes/NotesV1.storedata on the MacBook Pro. The note was still there hidden between various other control information. The note itself appears to be saved as html, so you can try something like this (in terminal):
- cd ~/Library/Containers/com.apple.Notes/Data/Library/Notes
- strings NotesV1.storedata | grep body
Each note that is stored in the file showed up on a separate line. Interestingly, a bunch of notes I had actually deleted also appeared in the list.
It is not a pretty way to get access to the notes, but at least I have managed to find the telephone numbers I needed again.
I hope this helps someone.