I can play a whole song in my head, and then realize that I don't know the words, and when I try to get the words out of the song in my head, I can't understand

I can play a whole song in my head, and then realize that I don't know the words, and when I try to get the words out of the song in my head, I can't understand them, because my brain only committed the musical parts, not the lyrical parts. I can even hear the vocals, they're just gibberish until I make a conscious effort to memorize them.