Okay, maybe you just solved it. Even though I don't remember the last time I played music on my phone, I went to the app I'd likely use if I did and started some music. Then I stopped it, turned everything off, and closed the app.
After my screen went black I checked again and, Voila! Just like you said, that screen was gone and all is back to normal.
Many thanks, my friend. Sorry I'm so ignorant sometimes....