There was once a great Chassidic leader that swayed back and forth very much during his davening and his students asked why he needed to sway so much. He asked them if they saw a person drowning and he was moving his whole body to stay alive, would anyone ask why his body is jumping around? Of course not because he is trying to stay alive. The rebbe said the same is with his davening. When he prays, he is praying to stay alive like someone drowning.