Dreams

What is a dream?
How do most people dream?
Does everyone dream, or is it just some people?
What is the difference between a literal dream (one that you have while you are asleep) and a metaphorical dream (a goal which you wish to accomplish, or a place you wish to reach)?  Can they be closely related or are they always separate?
Are dreams important?  Why?
Is there any significant symbolism in dreams, whether these dreams are literal or metaphorical?
How deeply do you have to sleep to dream?
Are there any side-effects from dreaming?
Is dreaming a side-effect of something else?
Do people remember their dreams always, often, sometimes, rarely, or never?
What is the significance of a recurring dream?  A recurring theme?