Gharib
I want Khilafah back
(al-An`am: The Cattle) 125 And whomsoever it is Allah's will to guide, He expandeth his bosom unto the Surrender, and whomsoever it is His Will to send astray, He maketh his bosom close and narrow as if he were engaged in sheer ascent. Thus Allah layeth ignominy upon those who believe not.
brother, I think It's lack of oxygen. just like those who climb mount everest, as much as they ascend, the amount of oxygen decrease.
however, We are not talking about hights here, we are talking about prayer , so when someone strive to concentrate in his prayer and try hard to avoid thinking about secular affairs ,the bosom shrink and get narrower due to embarrassment, therefore you may yawn to satisfy your body need of oxygen.
The same can be said for feeling bored, annoyed...
so may be satan has a role in this issue, he try to disturb you during prayer by grabing your attention to other issues, so your prayer become meaningless, so you start to feel boared or embarrassed or annoyed unwillingly.
Salam brother, you can go to the following link if you wish to read Ibn Kathirs commentary on the verse:
http://quran4u.com/Tafsir Ibn Kathir/PDF/006 An'am.pdf