Hi. For me my hypochondria probably started to start at age 7 or 8 when I developed some kind of rash on my neck, and thought I was going to die. The fear at the time was easily overcome by reassurance from my mom/dad. Further on I had a few hypochondria attacks when I was 12/13 thinking I had cancer (by then I knew that it existed... and probably thought it was the worst disease one can get) And I also got hypochondrias about malaria, plague, aids, etc... Many times I had minor attacks regarding appendicitis. Up until age 14 or 15 I started getting major cancer hypochondrias and ever since cancer was the major issue. I think that our brain automatically assumes the worst, and in our case it's "cancer".
My parents were generally nice and supportive, no exposure to death in the family when I was young. However, television, teachers and misrepresented common sense might've contributed to this.
One other thing that is (i think) contributing to this is self-consciousness. I think that I want to feel accepted and be "perfect" and "disease-free" so that people will love me and so that I can get a girl friend. Many times when I get a hypochondria, I think that girls will not like me anymore because of that specific thing. This sucks too.
The most things I have found to be effective against this are: Ignoring symptoms (after checking once with doctor), absolutely no self-checking, only looking and admiring, reading positive articles instead of negative ones (e.g. this forum), writing down a list of things on your mind. I think a great deal of "relapses" is due to zero-memory, and the fact that we forget that initially right after being reassured we felt OK.
The thing that scares me at this stage is the idea that this hypochondria beast is still sitting on my back and can wake up any minute, e.g. from a sensation or something. But while in a hypochondria attack, I think the most scary part is pain/death/evolution of symptoms and/or physical appearance. Like mentioned in this forum before, remember that Cancer is highly over-rated. People don't think of it as a preventable disease, however, if you look at the statistics, many cancers that constitute the large percentage of high mortality rates are preventable (e.g. lung, colo-rectal) and just a couple of others fill up the rest of the top percentile. Most cancers are not that common. (check out canadian statistics:
http://www.cancer.ca/ccs/internet/standard/0,3182,3172_14279__langId-en,00.html)
Hope I've helped.