Why do our loved ones come to our dreams after they are dead ?

Many say that they see their deceased loved ones in the dreams. 
                   
                     Many of us feel that the reason behind such dreams is ... we love them and it's their memories which we see in dreams. But such dreams have to be interpreted in a different way.

                     We do many regular things in our day-to-day life. But there are certain things which we feel that they will not be liked by our beloved ones. Such things when we do, our mind involuntarily expects  some comments or opposition from them and when we don't hear such comments, our subconscious state feels that something at that context and at that  point of time is missing. So, we get a feeling when we sleep that our loved ones come and just go like that., and hence conveying a message to us.

I have a supporting example for that:

                     My grand mom used to wake me up early in the morning and I used to revise lessons everyday. She always used to think that one should get up early, do their routine work on time and go to bed early in the night. If I didn't follow that, she used to be upset. She passed away in 2007. But, even today I get dreams regularly early in the morning when I sleep lazy even at 8'o clock. She comes to my dream.. just smiles and goes. My subconscious minds even now looks for those yells, screams etc at 6'o clock in the morning. It is a sort of warning she is trying to give me and expecting that I should get up early in the morning, study well and be a good student.

                     So, in order to keep my grand mom happy, I should get up early and be sincere... but, if I do so.. she will never ever come in my dreams which I think should never happen...