The next time you are having a "realistic" dream, try the following: (1) Look at peoples' hands. In a dream, the hands will always be misshapen, like a cartoon character. Typically the fingers will be out of proportion with the mid-fingers being longer than they should.... Or they will only have 3 fingers and a thumb. (2) Pinch your nose shut and try to breath thru it. In a dream, you will continue to breath normally thru your pinched nose.

You will remember this when you are awake, and will have confirmation that it was only a dream.