That is a question for my subconscious mind to answer. Unfortunately it refuses to communicate clearly on the subject. That's a bit frustrating and dare I say disrespectful seeing as it is actually me.

Sometimes they are coded messages from the ether world if you believe in that.
Sometimes it's our subconscious processing what our consciousness cannot.

Your dreams are thoughts occupying your mind in order to keep it alive. Thoughts are electrical impulses, and when these stop youre classified as dead. The reason why they're so jumbled up is because parts of your brain is in sleep mode, busy to repair and organize, while the parts of the brain that creates your dreams are left a bit on their own. The detail and realism of your dreams depends on how awake your brain actually is during sleep, the more detailed it is, the more it's communicating, and the worse sleep you're ultimately having.