UI Builder Page Corrupted--Please Help Me Recover It!

[Velma]

My UI Builder page--the one I just put a LOT of work into, has something corrupted. As I was working this morning, I added a Container and it didn't show up in the component tree. Huh, I was sure I added a Container. Added it again, didn't show up (showed up on the right, I renamed it, but it still didn't show up on the tree). Tried to see if it was in the wrong place. And the tree disappeared. Under variant name (with a diamond icon) is nothing. The components are in the middle panel but nothing can be selected/modified. The config panel is stuck on Page Configuration. Data Resources are there. Client Scripts are there. Client State Parameters says I don't have any--but if I click Add they show up again. If I open the page up in run mode, everything is there and functions. PLEASE HELP ME recover my page. Is there some way I can access the components in the platform, copy into a new page? Troubleshooting tips somewhere? 

[Velma]

Thank you so much, @Brad Tilton, you have given me hope. I have found the table in the platform, and found the record, and then I have remembered that you can actually open this from the page itself, Menu/Developer/Open page definition. I don't know how to add the versions related list and how to revert, but I will look for documentation (if you know where such documentation is, let me know). If I were to copy out those four big pieces of JSON and analyze them (in VS Code, say), might I find the issue? If I were to copy out those four big pieces of code and put them into a new page, would that mostly create a matching page? If I find the version history, could I revert by overwriting the JSON in the current record? 

[Velma]

Thanks again, Brad. I learned how to add the Version History and how to revert. However, I don't have whatever permissions I need to do that in the automated way. So I copied the XML from the history record I wanted, edited out the Composition section, and pasted it in to replace the Composition section that was there--looks like I am back in business. However, earlier I tried just adding a couple of components to another page to see, and that worked fine, until I logged in again later, and then it was broken too, and had to be fixed too. So possibly something is not right with my "experience" or my application or my ServiceNow instance is having problems. I guess I will find out... Meantime, I can't use the diff tool that is there either, so I guess I shall find one so next time this happens I can see what broke specifically.