Yawning and Tears

I've been yawning a lot today, and every time I do, tears begin to flow... Why is that? What is it about yawning that makes my eyes water? It's really hard to read my computer screen while I have tears rolling down my face. Not to mention when Josh Miller walks by my office and thinks I'm crying. (It's kinda embarrassing) If you know how I can stop this, please let me know.