I do my work digitally these days, so it's rare for me, but back when I used to draw on a drawing board, I drew entire comics lying on my front on the floor. One of them was a finalist in the Tokyopop UK+Ireland Rising Stars of Manga!
(Yeah this was a long time ago).
My advice would be to get a decent lightweight drawing board. I love Rotring ones personally. Other than that... I dunno, there's really no reason you can't draw well while lying down.