Emotions

How is it that i can be happy as anything one moment, and then the next be as opposite as you can get?  What is that about?  

How is it that something i feel fine about at one point, can suddenly make me feel completely horrible?  Am i in denial when it's fine, or wallowing when it's horrible?

And can i get to a state where i'm happy and fine without the switching happening?

I'm really hoping that this is hormonal.