Oneiro, I agree with everyone that's come back at you. I'll not repeat their arguments.
But anyways, let's stop scaring the OP and do something useful.
DramingDove: As said before, it's simply the realization that you are in a dream. Once you realize it, the awareness pretty much makes you conscious. Which is why you then have the ability to take control of the dream. The way I would define "control" is something like "consciously making decisions in your thoughts". So if you slot that all together, you'll understand why Lucid Dreaming is a very real and possible thing.
Control is only a possibility in lucid dreams, you aren't magically able to know that you have the ability to control is, which is why a lot of people who don't understand Lucid Dreaming will end up just going along with what is happening. They will make slight decisions, but nothing which amounts to your normal perception of control.
Anyways, I hope you understand it, and I hope you decide to try it. It is such an amazing feeling to have that awareness in a dream, even if you don't take full potential of control. Somehow you still get an amazing sensation. But taking control is just truly amazing. The biggest cliche, yet my favourite thing; flying. It just feels so good to be in the air with the wind against your face and a slight feeling of a G-force in your stomache.