Look at your trash in the Gmail account. Maybe they ended up there.
If you can't find them there, go to Settings - Mail, Contacts, Calendars - Gmail (the account), and disable Notes there. Force close the Notes app. Enable Notes for your Gmail account again. Wait for a few minutes, then open the Notes app and search for the lost notes.
J.A. Thanks for the suggestion, but no luck. Seems like I've had a number of strange things happening on my iPhone5 lately, all since I started backing up to iCloud. Think I'll go back to iTunes backup.