Do you think the position of your body affects your level of productivity?

DISCLAIMER: Let me state that this is not an invitation for sexual innuendos! Behave, people.

Personally, I feel like I do better work when I am leaning forward.
For instance, I can’t seem to write a paper while laying down.
Are there any other productive forward-leaners out there?
Or other positions of preference? [Please read disclaimer before answering.]

Is it some kind of evolutionary throwback?
Because we’re natural hunters and our eyes are in front?
Or simply a propensity developed over years of working at a table or desk?