Explanations can't really do it justice. It's almost like an extra sense, a sense to "see" music. Like some people can see auras I suppose (I wouldn't know as I can't see auras) but for me to try & explain what I see. Imagine looking at a brightly lit room with a lot of items in it. Suddenly close your eyes & you can still see the after image. Now make that after image more vivid colours & have it move & phase in & out. Have it move towards you & away from you in a recurring loop that's difficult to pull out of.
As I said, it's hard to put into words!