I also have trouble sometimes "completing" a yawn, and the excessive need to yawn. I was at my Chiropractor's office getting an adjustment on my neck, and he noticed me trying to yawn. I noticed him watching me, so I explained my issue. He said there was a vertebrae out in between my shoulder blades and it was pressing on a nerve in my back that was triggering that response. He gave me an adjustment, and within a few minutes, the problem went away!
My only issue is, I don't have the money to go to him every time I need to, so I just hope for a morning where I wake up and something fixed itself in my sleep
