This has happened to me a lot. Once I heard a unreleased Em verse, it had multies and EVERYTHING. It was amazing. Another time I heard "Almost Famous" but with his Relapse accent. And most recently, about 2 weeks ago I heard a Eminem chorus on a Eminem beat lol, I was like "damn this is fucking dope!"....I tried to remember it but couldn't. I have also heard a very poetic Nas verse lol.
I don't understand how the mind works that way? How come we can hear that shit in our dreams but can't think of it ourselves? Wtf.