I so feel you on this. Can't even count the times lately that I am fine, happy, high, and in a matter of seconds crying. I have never been a big crier so I can see what you mean (especially when it isn't necessarily accompanied with depression). And I know how distracting it can be. I have a huge presentation to do too and for the life of me cannot focus on getting done what I need to do, b/c I'm too distracted by my unruly emotions. Wish I had advice to give, but all i have right now is understanding and empathy...
-Valerie