I have only once projected out of my body lying on my back and it was not even a long projection. All of my OBEs happen only when I am lying on one of my sides. It is very uncomfortable to stay like this for long and sometimes (most of the times) I give up. But if I stay like this more than 10 minutes I always feel the vibrations. If I do it early in the morning I have no problem to leave my body. I don't know why but in the evening (probably because the mind is more busy) even if i get the vibes most of the times it's hard to leave my body..