My leg goes num while drawing

Nerono

https://www.youtube.com/watch?v=wUEl8KrMz14 While Drawing I know you should have the board slanted to minimize distortion, but by doing so I make my legs go num, as seen in the position draw on paper, I am looking for advice on this topic, thank you (I know as seen in this video you should stay active, wake up and move every 30 mins and also get hydrated but the numming is a serious problem because it hurts the blood circulation and nervous system leading to damage at the leg area, thank you for your help )


Double P.S.
The light in my room is really annoying, its really bright and hurts my eyes after a while, also it makes me cast a shadow on the board while drawing (its above me), I assume getting a light source from the side could be helpful but yet again it will hit directly my eyes, which also be annoying, any output on this subject?

whats_true

Why not stand and use an easel and use a clip on light on top? 

Nerono

Huge, which means it's not portable and also uncomfortable to sit and draw