Falling asleep is like having two preset radio stations
Wow, many thanks to a friend who helped me out with this analogy.
What I go through sometimes when I go to sleep -- as in last night's dream sequence -- is what would happen to you if you were in a dark room, listening to a radio station with your eyes closed, and then someone presses a preset button and changes the radio to another channel. Immediately you are listening to a totally different broadcast.
Now suppose that you are awake, this radio is in your control, and it has these two preset radio stations available to you. You have two choices: you can listen to this new station, or you can listen to the previous station, but you can't hear both at the same time. The first preset station is this physical world, and the second preset station, well, that's something else. Since I'm not really asleep I have a problem calling it the dream state or lucid dreams, but that's probably how most people would categorize what I hear or see.
Many thanks to my friend ... as usual, there is much more to say here, but that is a terrific analogy.