Yawning excessively happens when the act of yawning occurs frequently or in close succession. When you yawn, your mouth opens and you take a long and deep breath. It may also be triggered by viewing someone else yawning.

The exact reason of human yawn is unknown but common causes are here:

Physical causes

• Changes in the cycle of sleep-wake
• Medication side effects
• Cardiovascular disease
• Electrolyte imbalance
• Poor blood flow through the veins
• Hypothyroidism (Low creation of thyroid hormones)

Psychological or emotional causes

• Stress
• Depression
• Boredom

Life-threatening causes

• Stroke
• Seizure
• Exacerbation of COPD (Chronic Obstructive Pulmonary Disease that includes chronic and emphysema bronchitis)

Excessively yawning may be the sign of sleep disorder like sleep apnea and may also occur in the presence of heart disease.