yawning/stretching during meditation

Hello

Firstly I would like to share that NSR is a beautiful thing, I started NSR in April 2007 so i'm not even a year old with it and I feel really great because of starting it. I am hopeful that as the years pass it will give me even greater satisfaction and insight into living my life.

I have a question about yawning, recently I have seemed to have developed a routine of yawning during meditation that is not frequent during the session but usually occurs when the session either begins or ends, I think it may be a kind of 'nervous excitement' yawn due to the anticipation of diving within, maybe it's a stress release in itself, maybe you could explain how and why this yawn routine might be present?

best wishes
Kerry