Many agree that yawning is a reflexive deep inhalation caused by decreased oxygen levels in the blood, and is most often associated with sleepiness or boredom. Excessive yawning (1-4 yawns per minute) is associated with a variety of conditions. There are two things that happen when we yawn, those being that we open our jaw wide and we take a very deep breath. This only happens for a moment and creates a tremendous pressure in the lungs. Although some scientists offer the low oxygen hypothesis, others believe yawning may be:
Yawning can also be the first sign of what is called the vasovagal reaction. Potentially adversive stimuli, such as needle pricks or even generalized anxiety about some future event, can lead to increased activity in the vagus nerve. In some people the increased activity can cause their blood pressure and heart rate to fall. If the reaction is mild, these people may yawn, or feel apprehensive or restless. In more severe cases a person can exhibit dizziness, nausea, palpitation or even fall into unconsciousness.
Excessive yawning can be caused by a vasovagal reaction and may indicate a heart problem.