I started keeping a dream journal recently. I've found that since I started it, I am dreaming more frequently and I'm able to remember more of what my dreams are about. It's like a knock on effect. I'll start unraveling them and there are often common themes that they involve. It's actually quite interesting.
I don't know how accurate it is to say but I think I can only dream things that I have a reference point for. What I mean is that I dream usually about the things that I have directly experienced. I have dreamt about far-off places that I must have seen in movies or on TV.
Going by that, I wonder what people of years gone by would have dreamed. They couldn't dream of stuff they've not seen so I wonder if their dreams were as interesting as ours are now. It's an unanswered question that I'll never know about. I wonder of Freud ever published the dreams of his patients. I could Google search it and I daresay I will but as of writing this, I haven't.