Yawning involves opening the mouth involuntarily while taking a long, deep breath of air. This is usually done as a result of drowsiness or weariness. Excessive yawning is yawning that happens more often than would be expected, even if drowsiness or weariness is present.
Yawning is a normal response to fatigue and drowsiness, but excessive yawning can be caused by a vasovagal reaction. This reaction is caused by the action of a nerve, called the vagus nerve, on the blood vessels. It may indicate a heart problem.
Normal yawning may happen when someone else yawns.
Drowsiness or weariness
Disorders associated with excessive daytime sleepiness
Hermanowicz N. Cranial nerves IX (glossopharyngeal) and X (vagus). In: Goetz CG, ed. Textbook of Clinical Neurology. 3rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 13.
LeWinter MM. Pencardial diseases. In: Libby P, Bonow RO, Mann DL, Zipes DP, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 70.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.