Studies have proposed a number of reasons behind yawning contagion. Some suggest contagious yawn is a sign of social empathy. Some consider it a protective mechanism to make a group more alert. Some regard it as a social signal signifying sleeping times.

I'm ridiculously suggestible to yawns. I've had seven yawns when I write here. Rather than a sign of fatigue or boredom, my yawns are more a relaxing behavior that relieves anxiety and stress, or at least a physiological attempt to relax. Physiologists describe the yawning process as:

A yawn involves a deep inspiratory breath and slow expiration, accompanied by wide opening of the jaw, and sometimes by limb-stretching and lacrimation. The bronchial stretching on inspiration stimulates a cholinergic response that reduces peripheral vascular tone, thereby increasing peripheral blood flow. Venous return is also increased by the drop in intra-thoracic pressure. The blood-rich lateral pterygoid muscles (involved in jaw-opening) and the soleus muscle (leg-stretching) also contract, expelling blood and increasing blood flow to the circulation.

In my layman's view, yawning gets me more oxygen and slows down my heartbeats. Based on personal experience, I surmise my suggestibility to yawning is a subconscious reaction to potential stress. This also explains why I'm more suggestible to yawning in the English context than in Chinese, my native language.