I am of the belief that people that have passed on find it easiest to "reach" us when we our conscious mind is not in control, such as during sleep. It sounds crazy if you aren't open to such ideas, but I have heard so many stories of people having dreams of dead friends and family. These dreams are usually different from regular dreams in that they see more "real" than a regular dream. You probably really are connecting with the energy/soul/spirit of your grandfather while you are sleeping.