It's like being devoid of any more emotionally uplifting thing, such as something so beautiful you smile and cry at the same time. Any such thing is sucked out of you, like a vacuum just had a go at your heart. It's kind of like when I get that eczema-like thing on my right hand when I wash my hands too much and/or forget to put on my medicated lotion. Except it's around my heart.
It starts when something happens you don't like...and then the little thing start to irk you, and then you feel like everything's gone wrong. And then you can't remember the last time you felt happy. It's just one of those days.
People around you tell you not to be so grumpy, but all you feel like to doing is sitting around feeling sorry for yourself. Or perhaps, to cry.