As stated by funkstrman, do not move whatsoever. It helps you lose sense of your physical body, and can be quite similar to meditation =) I personally lay on my back -- it's easier to refrain from moving this way, as all of my body is just resting on the bed itself -- compared to when you are laying on you're side, where one side of your body is putting pressure on the bottom side.

I would try laying on your back a few more times. Post your results if you do this -- I'd be interested to hear how changing one's normal sleep position would effect their success at WILDing.

Best luck to you! hail WILD