Does anyone know anything about dreams?

I dont usually believe in the whole dream meaning thing but last night i had a dream about my dead grandad who i was very very close to. I could see his face it was so clear and it was certainly him, strange because my dreams i normally know who people are but cant see them or they are not clear. We were at a garden party at my parents and he was sitting in the chair and we were staring at each other and he was smilling and laughing the biggest smile. My 3 year old son woke me up and i was devistated i wanted to stay in that dream with him so bad. He has been gone for 4 years in February. It felt so real like he was really there with me, this is the first dream i have ever had with him in. Thanks for any answers..