Yawning is the involuntary opening of the mouth while taking in a long breath of air. Yawning is associated with sleepiness or drowsiness. Almost anything that causes drowsiness, ranging from tiredness to certain medications, can lead to yawning. Conditions like sleep apnea and restless legs syndrome can cause yawning due to daytime sleepiness. Excessive yawning is yawning that occurs beyond the amount expected even for someone who is sleepy. A vasovagal reaction is a process in the body that can trigger yawning. It can be caused by a heart attack or aortic dissection.