I've had a pretty fucked up relationship with dreams.
Firstly, this happens to me ALL THE GODDAMN TIME. Everytime I dream a dream nowadays I start off just fine. Could be a bad dream or could be a good dream, doesn't matter. Halfway through the experience I become self-aware. It's like you're driving down Thunder Road in Greased Lightning at 88 MPH, about to turn the corner for a victory lap,
Then everything goes into bullet time.
And I suddenly realize "Hey, this is a dream".
From then on, I let the dream play out, but if I don't happen to like where things are going, I just rewind and take a different path, like a multi-choice adventure book. Even when I'm dreaming I realize dreams are no fun if you control every little detail.
But this just happened to me recently, and it kinda freaked me out.
I woke up from a peticularly vague dream, but as I was getting up and going through the routine of getting ready for work (5:20 AM), the dream kept playing uninterrupted in what felt like a fog in my head. I was moving around and doing everything right, but it was like the theatre lights went on and the doors were opened, but the movie kept playing. It stopped about 15 minutes later, but after I realized what was happening, I felt pretty dumbfounded.