I picked up the following question from a post about dreams over at Pan's Island:
"What are your thoughts on why we dream the things we do and why some dreams just stay with us?"
The way I see it, dreams are the poetry of our subconscious or semiconscious mind. The dreams that stay with us are the ones that really made a deep impression – just like with quotes and moods that sometimes remain with us long after we have read certain books. They may have been wonderful, or scary, or just thought-provoking or mysterious - but somehow they touched us and left a mark.
When I sort through my bookcase sometimes, or look at the reading list I've been keeping on my computer over the last few years, I usually discover some books that I can't remember at all from their titles, even though I know I read them. With others, I may have forgotten most of the details of the plot, but I can still recall the mood they put me in, or "pictures" they made me paint in my mind.
At other times, sorting through deskdrawers and notebooks, I have come across old notes that I made about dreams in the past. Sometimes the dream comes back to me quite vividly, just from a glance at these notes. Sometimes I keep staring at them and wonder: Whenever did I dream this?! I have no recollection of it at all…
With dreams, I suspect that the ones we have managed to work through and understand – to lift, so to say, from the subconscious to our conscious mind - are less likely to keep coming back to us in the night; unless our subconscious finds them worth recycling again to remind us of something. Dreams that keep recurring usually do so either because there is still something lacking in our understanding of them, or because we need the feeling of recognition they may be able to provide.
Pan's Island also mentions the Harry Potter books by J.K. Rowling. These books are full of dreams – Harry has a lot of them, and I get the feeling that Rowling must have done some pondering about the nature of dreams, too.
In the first chapter of the first book (Harry Potter and the Philosopher's Stone), Hagrid comes riding on a flying motorbike, bringing baby Harry safely to the Dursley's house. Between the first and second chapter there is a time gap of nearly ten years; we then meet Harry as a boy of nearly eleven:
He rolled on to his back and tried to remember the dream he had been having. It had been a good one. There had been a flying motorbike in it. He had a funny feeling he'd had the same dream before.
If my memory serves me right, after Harry met and got to know Hagrid (the friendly giant comes again to his rescue, on his 11th birthday, to introduce him to the Wizarding World), this particular dream about the motorbike is not mentioned again. But other dreams, less pleasant, do keep haunting him – until Harry is "through" with whatever was or is behind them…