But the situation here is plagiarism- it is the same song, whether I knew it or not.
Believe me, I am familiar with the fear that a long-buried tune has popped ready-made into my mind. (Worse- just about the time I have the tune memorized I get to feeling just about sure that it is someone else's song- I think that's because it's beginning to sound familiar to my poor little brain. Oh, woe.)

This is different. Ah, well, I'll chalk it up to experience- nothing's wasted, right? Thanks for the responses. Ebbie