Q&A: What's causing my constant yawning?

I seem to yawn a lot. What could cause that? —M.N., Charlottesville, Va.

Since yawning is nature's way of getting you to take a deep breath, you should look into reasons for shallow breathing. The most common cause is sleepiness. Other possible causes include sleep apnea, a breathing disorder that can result in severe daytime drowsiness.

Certain medications, including SSRI antidepressants such as citalopram (Celexa and generic) and fluoxetine (Prozac and generic), can cause excessive yawning as a side effect. And the use of opioid pain relievers such as hydrocodone and oxycodone—or the withdrawal from them—can lower your breathing rate and trigger yawning. So can the sensation of a very full stomach after a big meal.

Finally, yawning is "contagious" and has a high rate of suggestibility—so choose your company carefully.