I have a very vivid imagination. Always have had. The trouble with a vivid imagination is that it imagines things you don't really want to consider, and then you can't get them out of your head.
Why do we always imagine disasters? Crime has been really bad in Oakland lately - but I'm a seasoned urban paranoid: I don't walk at night, or with an iPod plugged in, or while talking on a cell phone (all behaviors that increase your likelihood of being mugged). Why then does my imagination create detailed mental scenarios in which I'm being mugged by 10 armed street thugs? (Because, of course, somebody in my neighborhood was mugged by 10 armed street thugs a couple of weeks ago, while walking home from BART at 10 o'clock at night...) I carefully avoid situations that might get me into trouble - why do I build such detailed mental images of stuff happening to me?
And then there's "medical student syndrome" - you know what I mean. You read about some disease in the newspaper and the next thing you know, you're convinced you have the symptoms. My imagination is convinced that I'm developing some incurable disease that my HMO won't catch. In fact, all my blood tests come back normal and my cholesterol is great (result of going to the gym multiple times a week); the worst thing wrong with me is probably my asthma.
In order to reduce my car insurance premium, I'm taking a "mature driver's safety course" (I think I'm the youngest student in the class). After the first session I'm now convinced that my peripheral vision is shot, my reaction time is practically nil, I can't drive at night, and I'm going to lose my driver's license and have to depend on the Bay Area's crummy public transit. Considered rationally, I'm actually a good, careful, defensive driver; but my imagination is at it again.
It was worse when I was younger; my sister was convinced that clairvoyance ran in the family and that she, and our late aunt, both had it. So of course I wondered if I had it. My parents used to take long driving vacations across the country. While they were gone, I would imagine all sorts of horrific things going wrong with them (car accidents; floods; armed robberies), and then I'd have to take emergency time off work and race to their rescue. These mental images are very real - they trigger adrenaline rushes. Your pulse pounds, you start to sweat, you go into flight-or-fight mode.
After a while, I realized that none of the things I imagined ever happened; I'm a good, careful, defensive driver because that's how my father drove, and that's why he never had any trouble. People who believe in clairvoyance simply haven't kept the records properly - for every disaster they saw coming, they also foresaw fourteen or twenty-seven disasters which never happened. But nobody remembers the clairvoyant predictions that never panned out.
Also, nobody ever seems to be clairvoyant about good things. If clairvoyance is real, why would you not foresee good luck as well as bad? But you never hear about anyone who had a successful premonition that he'd get the good promotion, or win the vacation cruise to Cabo.
When you name something you control it; I finally came up with a name for this syndrome. I called it "manufacturing monsters"; and then I could say to myself, "You're manufacturing monsters again, stop it." And most of the time, that would stop it. In fact for many years, I had only minor problems with it.
Then I hit menopause, and damn if it didn't all come back. But don't ask me - I just live in this brain, I don't understand it.