I agree, M.J.: I don't think Plato or Aristotle would grant "art" status to sitting. But in a way you aren't talking about sitting; you're talking about stillness, right? And attention? Those seem most certainly to be forms of art, and ones we'd probably all do well to cultivate.

I'm sitting right now, but tapping away at my computer in avoidance of sitting and grading more final exams. There's nothing artful, contemplative, or transcendental for me in this moment, I assure you.

Lovely piece. Write on, my friend!