This is a fairly common occurrence when I'm trying to initiate a lucid dream through WILD technique. I'll be laying there and I can feel my body drifting away while my mind if fully aware of what is going on. I'll be drifting in and out with different visions when my arms will either go into the air and flail about or the will come together as if I were trying to grasp onto something in front of my chest.

Has anyone else experienced anything like this or know why this might happen?