This is the first time my mind had noticed a loophole in my dream and realized this might be a dream! This is exciting. You see, even though I did think this might be a dream and decided to scream, in the dream, I was pretty sure it was real - when I started screaming I didn't think it was going to work, because I was pretty sure I wasn't in a dream. It's pretty scary.
This could be a step toward what they call lucid dreaming - realizing you are dreaming while you're still in there, and try twist the plot as you wish and have fun. It is said it could be used as a self-healing device, but I have never been able to do it.