I have had dreams where I have taken up exactly where I left off, but never for four years. More like a few nights at most.

That sense that the dream reality is a consistent, real "place" that you visit while dreaming - I have that sense, too, but it doesn't cause me any trouble to switch between those realities (mainly because the dream reality is so different from "normal" waking reality that I'm rarely confused, and if I were, doing a reality check would straighten things out for me).

So I think what you are describing is normal but you are experiencing it to an unsual degree. And if you are worried about knowing when you are in normal waking reality, then its a bit of a concern.

It could be that your brain is simply gifted in dream awareness. But I wonder if its possible your unconscious is trying to work something out in the dream state. Have you had any traumas around 11-12 that could possibly be affecting your dreams? Do you sometimes hear voices that other people don't hear, as you are falling asleep or when waking up or at other times? How are you doing in school - any changes in your grades? Do you have friends you hang out with on a regular basis?