Layer has vanished

Type of device* : Laptop
Brand and version of the device: Lenovo Thinkpad
System** : Windows

I’m working on a multi-layered digital painting. Suddenly one of my layers has disappeared. All the work I’ve done on it – a lot – is gone. The thing is, it’s not really gone. I can still see it in the thumbnail for that layer. I tried moving the layer up to the top, in case something else was suddenly blocking it, but that didn’t help. I’m at my wit;s end.

* graphics tablet/display tablet/2-in-1 laptop/Android tablet
** Windows/Linux/Mac/Android, + version (you’ll find it in Help -> Show system information for bug reports)

Description of the issue (you can include screenshots):

I figured it out. Of course it was obvious once I went away from it and came back. I had accidentally set the opacity slider to 4 percent.