How many people out there have had an intense dream where they interacted with a deceased loved one? Almost everyone can recall having had a vivid dream like this that was so intense and tactile, they swear it was real. Statistically this most often happens within a week of the person passing. Psychological studies explain it as a coping mechanism for grief, giving your brain an outlet to emote when it may otherwise not be able to. This certainly makes sense in the United States, where it seems to be the trend to bury grief way down to be dealt with at a more appropriate time. I can remember when I was having to deal with the death of my father; It seemed like the most immediate goal was to keep it together to get through the funeral and all the other nonsense so I could finally just get to have some alone time to sit with my thoughts and process. And while the memory is a bit faded now, at the time I was having some dreams about my dad that involved conversations. In the dreams I knew he was passed away, so I hung on to the moment and took the opportunity to have some final conversations. And while upon waking I would feel very emotional from it, I did feel good about it. So I can definitely see how this idea is valid.
But, what about the flip side of that coin. Some people feel so strongly about those kinds of dreams they swear they are being contacted from the other side. There are certainly instances where the argument could be made. One close friend dreamed about his grandfather the night before he passed. His grandfather told him it would happen and that everything would be alright. Some might claim that it was subconscious intuition tromping the coping mechanism; but my friend had no idea that his grandfather was even ill before the incident. Others will get passed information about the future or people they have never even met. Intuition only goes so far, even as a scientist I have to admit there is more to it than simple coincidence.
To me the idea that spirits could potentially visit us in our dreams is a bit startling. Dreams happen within your own mind. To have an entity, even a loved one poking around in your head just disturbs me a little. There's quite a bit of stuff I have floating around in my ultimate personal space that I don't necessarily want my past lived family members checking out. The idea of that just seems a little far fetched to me, but an alternate possibility is that of astral projection. A case could be made that when experiencing these kinds of dreams you aren't actually dreaming, but sending your consciousness into another place where the veil is lifted. Mainstream science is lending more credence to the idea of astral projection and remote viewing having reopened experiments from the past with new perimeters. Many people have shown to possibly have the ability to do this. If spirits are real, wouldn't it be possible that your consciousness could share the same space as a spirit? I have spent allot of my time practicing lucid dreaming; it can be achieved through practice of certain sleep exercises. Lucid dreamers can usually exhibit control over their dreams and change the environment (I cannot, my lucid dreaming seems to work a little different than everyone else.) In theory it could be a form of projection; and if not a person could purposely summon up any number of spirits in their dreams. I for one would never want to do this, but I could see where one might want to.
No matter which camp you reside in; it's pretty universal that people always tend to feel better following the experience. I find it interesting that people never tend to come back in your dreams to tell you what an ass-hole you are, or how you screwed up. In my mind that makes a case for a more self serving motive for your subconscious. But, that's just me.