I had the same problem, and mostly fixed it by not leaning the head on the side. I used to draw with my head totally relaxed on the left hand, which also caused back ache and tooth ache when I kept the position for too long.
Posture is killer when drawing a lot of hours. If you still have troubles staying balanced, there's a lot of sitting solutions for people sitting for long times, as in office work (some use a table that allows you to stand, some others use yoga balls, or other chair solutions)