Unfortunatley, I was in the middle of editing a layer. Then, I got a server lost connection. Like I said it was brief. When I refreshed, I was logged out of the Joomla admin. Then, the page was gone. But, the confounding thing is I didn't even have the last saved version of this page. I did have a working draft up for a couple days. So the whole page was gone. I was suprised the whole page got blown up.
I think my reasonable user expectation was that I would at least get something that was saved previously.
For example, I recall updating a Squarespace site (not a huge fan), when I was actually logged out of it. I did some chjanges and hit save and it told me I was logged out and I lost my last edits because I wasn't logged in. I have no trouble with that behavior (serves me right), but if my earlier versions were simply destroyed, that would be most unexpected.
Sadly, my only recourse might be to recover my beautiful SP Builder Home Page on the event horizon of a black hole.
On the positive, I do like the SP Page Builder tool very much. I am hopeful I can recreate my page quite quickly now that I am more familiar with the tool.