How was I able to "see" images with my eyes closed before I was asleep?

[Shloom]

Very strange. I went to bed and closed my eyes. About 20 minutes after I closed my eyes in bed I was 95% sure I had not already fallen asleep. Even so, with my eyes closed, I was able to create an open book in my mind and on the left page I was able to make different images appear and disappear as I wished. Basically, at first I saw a picture on the left page of the book. Then I really wanted another picture to appear. First, the former picture on the left page faded out and then the new picture appeared, again on the left page. Every time for about 5 times when I really wanted another picture to appear, it did. And yes, I really saw the images, just as vividly and realistically as you are looking at your computer screen right now. However, at the same time I was 95% sure I was still laying in bed trying to fall asleep. What is this kind of experience called? Just very vivid imagination right before sleep?