Depression? I feel normal till I think about it then...

I had another topic describing how I felt but I need to ask a question. What is normal depression like? I feel normal till I think about it then I go on a huge downer, if its in my head but I don't completely think about my life etc I think anxiety and fear but not a downer because I'm forcing myself not to think how bad it is.

Obviously since the feelings are so extreme my mind makes me think of them every few minutes unless I'm with people. Obviously when I'm doing something my mind can't think about stuff so I like to keep myself busy, however then surely this isn't depression as I want to do stuff which is uncharactaristic of depression.

I think its the fear of feeling like this that makes it keep coming back, but when I think about it I get so depressed I just feel like there's no way out and really do want to just curl up and die. (don't worry, I'm petrified of death so would never contemplate suicide) I think the worst part is that I feel like I'm doing this to myself by continuing to think about it, I'm overran with fear.

So does anyone have any idea what this could be?