I definitely have extensive experience of mental health problems, my own and those of people I love..
I firmly believe that psychiatric diseases don't exist as individual entities. It's not like, say, diabetes, which has a specific cause and a specific outcome - mental illnesses are a cluster of symptoms which seem to go together and seem to follow a particular course and respond to particular treatments. It's all a continuum. There is no such thing as normal and no such thing as a specific psychiatric label in my eyes, apart from the fact that people love to give you labels..
There is no one cause either I think - it's a mixture of biology (your brain chemistry being out of whack, or an episode triggered by drugs, for example), psychology (stress, or childhood trauma, for example) and social factors (your support network, financial worries, housing etc) and there is absolutely no point treating one area (eg the biological aspect with antidepressants) without also looking at the other areas...
There certainly are clusters of symptoms that often go together, in what we call depression or mania or schizophrenia for example, and there are treatments that tend to work for people with these clusters of symptoms, but everyone is unique. And it's only a disorder or an illness if it affects you (or others around you) adversely, I think. And there is no such thing as normal :D
I've had depression for about 8 years now I think, with about 3 fairly major episodes resulting in a total of about 6 months off work, and I am currently going through a bereavement (which isn't classed as a mental illness but it's been far scarier and I have felt far crazier than I have during any of my depressive episodes) and I have had a partner who had a psychotic episode and a friend with bipolar disorder and another (several actually) with anxiety. Mental illness is scary, but it's so stigmatised still - it would be a lot less scary of people were more open about it and shared their experiences. So many of us will experience it at some point in our lifetimes.. I think the human brain just isn't "designed" to cope with the pressures of modern society...
Great thread Brimz, as a TDS mod and someone with a lot of personal experience I had to post :D I appreciate TDS can be quite US-centric, and it can be a lot easier to talk about your problems with people you know well, in the forum you know well (or vice versa sometimes!) - we have TDS regulars like there are EADD regulars, it just depends where you feel comfortable
