Here’s a new one… This afternoon in yoga our instructor caught someone yawning in class and called her out–not to reprimand her but to let her know she was dehydrated.
Yes, apparently yawning can be a sign of dehydration. And you don’t have to be sweating in a 90-degree yoga studio for this to be true. If you find yourself yawning at your desk, during meetings or in class, it might not just be because you’re bored.
The deal is that if blood volume is low–as is the case when you’re dehydrated–then the brain will receive less oxygen than it needs which will result in fatigue and… yawning.

can you just be tired? … or bored? because i am both of those yawny things
I am definitely NOT drinking enough water. I yawned a-bazillion times today. Gulping water now. Thanks!!!
Good lord, I really AM permanently dehydrated!