Is that just hypnagogia? Many people experience that before falling asleep, I could also do this while awake but with eyes closed, it is usually colors and shapes but not anything concrete.
It sounds similar, but it happens very easily with me and isn't so tied to sleep. That is, I can have full dream like experiences while still being awake and conscious of everything that's happening to me. Almost as soon as I close my eyes, even while awake and sat at a desk I see visualizations which can easily turn into complex fractals, many colors, I've always thought it was so cool.