if yawning is accompanied by other common anxiety symptoms, it may be due to an anxiety disorder. It is also associated with tiredness, sleepiness, stress and hunger. According to one theory, bored or tired individuals don't breathe as deeply as usual, taking in less oxygen and yawning helps to compensate for it.
Excessive yawning is yawning that occurs frequently (1 to 4 yawns per minute over an extended period of time), sometimes without any apparent reason. Increased yawning often precedes seizures and migraine headaches, in people with epilepsy and migraines. Yawning excessively may also occur in the presence of a heart defect or disease.