Some people, mostly older or superstitious in my experience, claim that we can be visited by the dead through dreams.

This has happened to me too. Once in a while I will see one of my grandparents, or sometimes both. It's very vivid, and they'll hug me. But it's a deep, comforting hug that I FEEL it. One time this happened with my grandfather and he said "Remember, you'll be OK. I'm watching for you."

I woke up bawling like a baby.

I think these things are buried in the subconscious, rather than being from literal spirits. Maybe something is bothering us. We need to be comforted, or reassurance, or a sense of safety. And who better to deliver these things than relatives we loved and trusted the most? I do believe it's a type of coping or stress management by the brain.