I also have noticed that sometimes you are in control and sometimes you just do things that imply control. Often, within a "lucid dream" I kind of go back and forth between these two situations.

I think that the main difference between these two states is that in a true lucid dream, your prefrontal cortex (the part of your brain that gives you free will) is activated. In normal dreaming, scientists have found that this is shut off during normal sleep, which explains why we have no control in normal dreams. Although it has not been tested (Why not?), I am pretty sure that in a conscious lucid dream the prefrontal cortex is activated. So in a "fake lucid", I'll bet that that part of the brain is still shut down, while the other parts of the brain know that they are dreaming.

Interestingly, I have had a few dreams in which I had complete control and will, but never figured out that I was dreaming. Once I was frightened because I thought that I was hallucinating and going insane !

TigrHawk, having your prefrontal cortex activated has a distinct sensation to it that is hard to describe. I can feel it strongest when I meditate on my breath...