Epilepsy, brain tumor, stroke, multiple sclerosis and liver failure are disorders that cause excessive yawning, according to Healthline. Bleeding in and around the aorta and a heart attack are other disorders that cause an unusual amount of yawning.
The most frequent cause of yawning is fatigue due to lack of sleep or a sleep disorder, explains Healthline. Certain medications that treat anxiety and depression can also cause yawning. To identify the cause of a patient's excessive yawning, a doctor may order imaging tests, such as an electroencephalogram or MRI. The electroencephalogram monitors brain activity and helps diagnose brain tumors, sleep disorders and brain issues, while an MRI helps assess spinal cord, brain and heart problems.