This has happened to me a couple of times, and I was wondering if anyone else has seen vague images when sketching. But when you go to draw the image it suddenly vanishes, but you had this sense of urgency to draw the image.
i get this alot, i will go to draw an idea in my head, or suddenlly see something in my mind. Then when i go to right it down, its gone. I believe that it may have been something that you saw a drawing of when you were younger, such as a chinese tapastry or something on the television. Then you think to yourself and that old memory comes out from the back of your mind.