Accidentally hit "Don't Save"

Are you saying you went days without saving your file?

How screwed am I?

Unfortunately, it sounds like 100%. I don't think that InDesign stores the crash recovery files when you don't crash. You can go look, though. I haven't used a Mac in a few years, but I assume they're still stored in Users/yourusernamehere/Library/Cache/Adobe InDesign/Version 20/ or something very close to that. Your Library might be hidden, but it's pretty easy to reveal it. It looks like you can still Go to Folder ~/Library and navigate to the recovery cache from there? I found a number of files in my cache with names like "DbTmpBunchanumbers" which I was able to rename file.indd and successfully open in InDesign. However, I'm fairly certain that they were all left behind from crashes, as there wasn't anything recent in there. So I am sadly going to have to stick with my Estimated Screwed Level of 100% for you. 

When you "days" of work? If you started this file days ago, you didn't save it at any point in the interim? I'd suggest both making the habit of saving all the time, and also of doing a fresh Save As every day.

I assume that it'd be saved as a Cloud Document if you had at any point whacked the "Save Cloud Document" button in the Save dialog, but it doesn't sound like you did that. There are some file storage solutions that can be used to roll back to previous save files - a correctly configured Windows file server, or Dropbox - but you still have to be actually saving the documents for this progress to be stored. 

No chance to get it back if you have not saved the INDD file.