How to wake a MacBook Air (2019) display after it suddenly goes dark (not sleep) for no reason in macOS Catalina (10.15.1)?

This has happened to me a few times since upgrading to macOS Catalina (10.15.1) and the root cause is unclear.

I am downloading something using Firefox, in push Firefox away to do something else, I go to use Safari — or a text editor — and then… Like magic… The screen goes dark… Not sleep… Just dark… And I can’t see the desktop or anything.

I know the underlying system is still up and running because if I SSH into it from another device/system I can see the OS is still alive and not hung. And in the case of the download, I can still see data being downloaded using the command line tool nload (which I installed via Homebrew). And past that the brightness controls on the keyboard still work… But obviously the screen is dark — and not turned off because of sleep mode — and I can’t see anything.

Now, under most circumstances, I would just say a few “choice” words, hold down the power button and wait for the machine to come back up via reboot. But this download is in progress so I don’t want to do that.

So what can I do to get the screen on my MacBook Air active and viewable again?

The solution is to login from another device via the command line, put the display to sleep and then wake up the machine.

This solution hinges on whether or not you have SSH remote login capability to the machine. But if you do, you are in luck!

What I did is SSH in from iPhone using a Terminal app and then run this command to put the display to sleep:

pmset displaysleepnow

When I entered that command, the display on the MacBook Air went truly dark. Then by simply tapping any key on the keyboard, the screen came back to life. And my download was not interrupted!

FWIW, I am unsure if this is a MacBook Air (2019) specific issue, a macOS Catalina specific issue, or some combo of the two or just something else. Posting specifics in case this helps someone in a similar situation.