My choral conductors and vocal coaches over the years all agreed on one piece of wisdom: don't move. I had a great deal of trouble standing still when I sang; in my college choir I won the "Most Animated" award. But as I joined smaller and smaller groups, I learned that every sway back and forth was energy lost, potential power you couldn't to apply to the sound. And motion is distracting to the audience, as well--an a cappella group shouldn't look like tall grass on a windy day.
I learned to stand still. Then I came to my synagogue, and stood among the congregation during prayer--and kept hearing the ghosts of my teachers: "Don't move!" But everyone else was swaying and, anyway, no one was listening to me. My sounds were private; this wasn't a performance.
But it wasn't easy to follow the orders of the voices in my head, because the entire congregation seemed to move in unison with one another's breath. There was no violent shuckling (like the stories of ancient rabbis lurching with such intensity that they ended upon the other side of the room), but rather a gentle wave across the rows. Eventually I started swaying, too, just a little bit. It felt subversive but good, and the rhythm of motion was like an instrument accompanying my prayer.
During services this past Shemini Atzeret, I found myself moving differently than usual, front to back instead of side to side. Suddenly I had a sensation of déjà vu: I knew this dance. I closed my eyes and saw sunlight streaming into my parents' bedroom window, and my father's silhouette as he wound his arms with tefillin. And then he swayed, back and forth, back and forth, just as I did this day while early morning light poured onto my tallit-wrapped shoulders.