In our ergonomics lecture we were taught to keep a neutral position where little to no muscle action is required to maintain position. I believe to follow this rule they told us to align our head over the spine. "Neck is neutral when weight of head is supported by spine." .... .....That being said I would find it hard to believe that this is possible to maintain the whole time you are chairside. So for what its worth I think I am going to attempt to keep my neck straight but will not die if I have to place some strain on my neck once in a while.