Why do you yawn when you're tired or bored?

Ok, so I know that when you yawn, it means you requirement more oxygen. So why do you need more oxygen when you're bored, or when you're tired?Why do you yawn when you're tired or bored?
Good interrogate Christen. When we become tired, blood circulation slows and pools in vienules (very small viens). We instinctively stretch our muscles to work and squeeze the vienules to push the pooled blood out to circulate again. (This function is adjectives hard-wired in the brain.) There is a great amount of blood circulation contained by the face, because this is where on earth most of our senses are. As funny as it sounds, yawning is a way of stretching the frontage.
Because like when your involved, your musles work hard. It works duplicate way when your bored or tired. its your body and musles relaxing. Or simply because your tired and necessitate sleep.
I guess because when you're bored or tired you usually aren't very moving.
i think it's probably that ur brain lacks oxygen when u r tired and u yawn so that u lug in more oxygen.