Yawns galore

At least when you yawn you are indicating to your interlocuteur  that you are not asleep. In my experience, yawns come in waves or, as I prefer to say, in books. My "book" is about 10-12 yawns, and anything above that number may be considered a bonus. It is only when you have made your book that you achieve an appeased state that may be conducive to sleep. So people who take offence at your yawns should in fact bear in mind that you are still actually quite a long way from sleep.