Looks great! I know what you mean with holding your breath and focusing so much on creative process that the grip on the pencil becomes painful. I often have my thumb numb because of how strongly I hold my tools :O I haven't found any cure for this bad habit of mine yet. Fortunately I learned to breathe properly, with a help of yoga classes and meditation, and it has worked wonders for me. I didn't know that Art Nouveau had a social aspect, thank you for this educational value :)
I learned to follow the breath using a Theravada Buddhist technique called anapana. But drawing isn't like sitting on a meditation cushion focusing on the natural breath coming and going around the nostrils. I'm making progress, somedays are better than others. I practice yantra yoga and it helps my stay bendable, which tends to go away when people age!