Greetings,
I’m new to Scrivener and am in the middle of NaNoWriMo. Day before yesterday I lost 1500 words, and subsequently (unsuccessfully) spent hours trying to find the work, then re-reading through Backup Information. I then did my best to re-create that work, added more, was confident all was in order when I shut down the program yesterday, only to find this morning…AAAAACHHHHH…most of yesterday’s work has disappeared.
We are on Yosemite. Help. 
Your words are likely still on your hard drive. Here are a few questions that might make helping you a little faster:
Do you use “Save As” to back up your work? Have you looked in all of the recent “Save As” copies for your missing words?
Do you store your project in a “cloud” folder, like Dropbox, iCloud Drive, Google Drive, etc…? Depending on the service, you may have a “conflicted” version of the file or files you were working on before the disappearing work. Right-click on your project and search for files with names that stick out from the rest (dropbox adds “conflicted” to a file name, for instance).