Well, in my Drafting class, we do a whole lot of nothing, so I put my head down and sleep every class. I'm always playing relaxing music (Bob Marley, The Moldy Peaches, Apples in Stereo, etc) and my mind wanders into thinking about things I want to do later that or on the weekend. As I begin thinking of something that involves a lot of movement, such as jumping a fence, I feel myself jump over the imaginary fence. I don't know if I'm actually jumping a bit or it's just my mind playing tricks on me.

Why does this happen?