[ryanhuff]

Having witnessed the process, something tells me that a significant portion of the pain is not caused by laying down. So, citation please.

[lotsofmangos]

I would like to cite Newton here. Specifically his work on gravity as it applies to motion.

[viraptor]

I believe parent meant that position doesn't change size. It may be faster, but one way or another the pain does come from pushing the baby out and potentially making lots of damage to someone's crotch in the process.