I was told the reason why we turn our heads away is because with Nikyo pins and Sankyo pins - it has something to do with the artery or something in your neck that when you turn your head to face the person pinning you will go unconscious. I remember Michael Williams Sensei told us something like that a month or so ago.
In short - don't face nage/tori when they are pinning because you'll put yourself to sleep very quickly.
Interesting. I know when I began Aikido I never turned my head away when being pinned, but I don't recall passing out. I will definately check this theory next practice.