What are these terrible moments?

The same thing happens to me. In my case I think I have a form of depression and I'm seeing a doctor next week (so nervous). if you can get your hands on it try to find the p.b.s documentary called "depression: out of the shadows" I got it on netflix. I've been struggling with these feelings for almose ten years and watching this made me feel like I could do something about it and that its a curable medical condition. Talk to your parents a counselor or even your family doctor about how you are feeling because trust me it won't stop happening on its own.