I wake up with a scrap of a song in my head pretty much every day. That's been dealt with here, many people here do but, sometimes it's a lyric or at least a tune I would swear I don't recognise.

Since I have only written the tune to a song three or four times in my life, I assume I have no particular talent for song writing and therefore it must be a sort of deja vu ( there should be another phrase for heard before,yes?), and somewhere in real life I have heard it. No idea how I would trace it though.