Sharing Dreams, Thoughts, and Emotions

There isn't a bunch of literature or study on shared dreams or emotions. Much more on telepathy, but that isn't the topic.
This topic is the question: How much of what we think is our own personal space is actually personal?
My reason is based on my own experiences and digging for possible answers. There isn't much literature on "dream walking" except some personal shares.
Having experienced a sudden onset of paranoia one day, I realized it wasn't mine, but my niece who was hiding from a mass shooter. It took some fancy meditation to figure out the source of that. Having been in other people's dreams, and gotten confirmation of the content, and that I was participating, it made me wonder how much of what we dream is actually our own? 
How much of daily thoughts, feelings or anything else are purely our own? How much of that is force fed from others?
So tell me what you think. I've been there and experienced it, so you aren't likely to change my mind, but debate and discussion open up new avenues of things we might miss when we experience things at a personal level.