Unity deleted 4 unopen scenes. How do I get them back?

I was viewing the demo scene in the Unity Particles example. One of them wasn’t working. So I re-imported the whole thing from the Asset Store. Part way through, Unity went black. I could still see the window and title bar, just nothing inside it.
A gray box flashed on the screen that said something about Not able to perform some action due to read error.
Then, the window closed, and I saw Unity splash screen, and then proceeded to re-import the entire project.

Except, all 4 scenes I have created are gone.

I haven’t restarted Unity, but there is no _EditModeScene in the Temp folder (only for open scene anyway).

It would make sense to me if it was 1 open file, but the 4 unopen scenes shouldn’t have been touched.

Where did they go? and how do I put them back?

Wow. Found an answer from 2013 that worked… just wow.

From: http://answers.unity.com/answers/600269/view.html

I deleted my library and held down alt when opening Unity.

I didn’t get a prompt to pick a project.

Instead, Unity stayed on the splash screen, did some work and then closed.

I opened it again, as I usually do from Unity Hub, and my Scenes are back!