Why do we yawn at Dihkr?

Peace be upon you Ô Qa’im Ale Muhammad (Qa’im of the Family of Muhammad), my question is: why man when he does Tasbih (Praise) or Adhkaar (The contemplation/remembrance of Allah) or Istighfar (forgiveness) and especially forgiveness, he starts yawning and having tears in his eyes, or also when we hear your Dhikr (remembrance of Allah) we have tears in our eyes, or when we are humble?