Re: I just found out I'm bascically an idiot
As far as a score changing, psychometricians have this easy to understand concept where they say one's observed score is equal to the true score plus error - classical test theory. The observed score in this case is 99 and that is the product of the true score (your underlying intelligence) and error - error could be anything that distorts your true score, from anxiety with the timing to your psychologist's incompetence in administration to the sound of the fan in the room distracting you during the test.
When you are given an IQ you should also be given a confidence interval related to that score. These are usually 68, 90, and 95% percent confidence intervals on IQ tests. This basically means that there is a, say, 90% chance that your "true" score lies between two numbers. For your score, and this is an educated guess, the 90% confidence interval would be 95-104 maybe. Low scores tend to have the second number closer to the mean and high scores tend to have the first number closer to the mean due to regression toward the mean.
All regression to the mean is saying is that a score far from the average, in this case 100, would be apt to be closer to the mean on second administration. Basically, for you this would mean if you redid some tests that you did poorly on, you would probably do better on those tests - i.e., closer to average on the perceptual reasoning index subtests. Sometimes though it is hard to say whether coming closer to the mean is because of true regression toward the mean or exposure to the test or procedure.
However, you can apply this same concept to essentially anything. For example, someone flies around a racetrack and sets a lap record - their second time is probably not going to be as good - i.e., it will drift back towards the mean. You could apply this to anything though, from ice cream cones sold in one month (a record for vanilla!) to a record setting number of Toby Keith albums. The next one ain't going to be that good. Basically, if you are winning at something, you would do well to quit immediately!