Do you see any sort of visual imagery when dozing off to sleep? Have you ever played a lot of some visually repetitive game, like Minesweeper, Tetris, Bejeweled etc? I find that if I play a lot of those (hours) then at night when I shut my eyes I can't get rid of visualizations of these shapes in my mind, it's even kind of annoying.
For reference, this is what happens to me. If I spend a few hours playing a particular videogame, its imagery "burns into" my mind - when I close my eyes, I can see recurring patterns from the game (like ground textures or UI elements); if I'm tired, that's an easy way to get me to high level 3 on the "starn scale". The effect disappears after I sleep for a few hours.
