This is going to be one of my very rare posts that has nothing to do with geriatrics, but since this morning I found myself frantically searching Google for the info above, I've decided to share what worked for me.
Let me start by saying that I did not find the answer on Google. What I found is "If the post wasn't published, I'm afraid it's gone." I also found instructions for retrieving a published then deleted Blogger post, but those didn't work for me because I had just deleted a draft.
Here's what worked for me:
1. Start typing "blogger" in your address bar, and your browser will start proposing recent webpages that begin with www.blogger.com. You'll notice that in the long string of URLs related to your blog, there is a blogID, and also a postID.
2. Start trying to load pages with different postIDs. Assuming you looked at your draft post recently, one of the URLs will reference the postID of your deleted post. In my case, it was the highlighted post ending in 072.
3. When I found the URL of my deleted post and tried to load it, I saw my post briefly, then it turned into this:
4. You can try to capture a screenshot of your deleted draft at this point. Better to retype it all than to have to recreate from scratch. But in my case, when I clicked close on the error message, my post was fully visible on the screen.
5. Copy and paste your draft, preferably to something other than Blogger. You'll keep getting error messages if you try to save the draft page on screen though.
6. Never forget that Blogger doesn't keep deleted drafts in a trashcan for you. This strikes me as a big flaw in the design, but there it is.
Hope this information is helpful to other beginner Blogger users out there.