Is it normal i can experience the beginning/creation of a dream?

I've been able to do this a few times over the past few years. I have never consciously tried to do it, I somehow just stumble upon it once in a blue moon. I often lie down because I am sleepy and want to take a nap, but I also don't want to take a nap because I have some work to do, or don't want to mess up my sleeping schedule etc

So I lie down, eyes closed, sleeping position. Usually there's a physical distraction such as my noisy computer, or the light remaining on. Now remember part of my brain wants to stay awake, yet part of it wants to sleep. What happens is after 5-40 minutes of lying there, I fall asleep, but *just*. I then wake up, but only just, eyes still closed, and somehow my subconscious brain doesn't get alerted that my conscious brain is awake.

Result? I start seeing random images being formed. Usually it is very abstract but just today I saw a window at medium-range distance. It was a window filled with very vivid and bright colors through it, surrounded by that darkness of having your eyes closed. But as soon as my conscious brain saw the window and I silently thought, "whoa that is interesting" -- POOF. The window vanishes and what I'm left with is the usual darkness when you have your eyes closed