So, the information I'll provide you comes from an article that I read in a health magazine. It's an interview with a danish specialist and researcher in dreams, who has cand.merc (masters degree) in psychology. The article is in danish and I thought it may be quite interesting for some of you, so I'm translating some of it to english. (I'm skipping the part with body temperature, blood pressure etc.)
The only source comes from this article, which is why I'm posting this on the "general" section, as sort of entertainment purpose instead. I'll edit and post the link to the (danish) article when the forum allows me to.. (Apologies if it's still the wrong section and my 'poor' translation skill.)
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What happens in your brain?
Overall the brain "slows down" when you're sleeping. However, parts of the brain actually more active when we're dreaming than when we're awake; such as the emotional part of the brain (amygdala and hippocampus), the long term memory, the brain's imaging center (the visual cortex), and the brain bridge which sits in the extension of the spinal cord.

What happens with your mood?
How much the dream affects your mood depends on how close you experience it, and how intense the dream has been.

What happens if you sleep on your stomach?
Some studies indicate that our dreams can be more erotically exciting when we sleep on the stomach. Conversely, the prone sleeping position can also provide dreams of being imprisoned or breathing problems.

What happens if your turn during a sleep?
A dream is often tied to the position you were in when you had it. So if your turn during a sleep, the dream can disappear from your memory. Similarly, it can come back if you return to your dream position.

What happens when you talk in your sleep?
Typically we do this when we have emotionally intense dreams such as nightmares or dreams with sexual content.

What happens if you're lacking in vitamin B?
Some studies indicate that vitamin B6 helps us remember our dreams better. However, our ability to remember our dreams is different. It's a mental ability that can be trained just as well as foreign words and terms. The more you care for your dreams, the better you will remember them. (But vitamin B6 can help you along the way)

What happens if you've quit smoking?
In the context of quit smoking, many get more intense and wild dreams. The explanation is that theb rain is in the process of repairing itself. Among other things, the balance of the neurotransmitter, serotonin, should be restored and is therefore produced in larger quantities than normal.

Women and children are better at remembering their dreams than men.
On average we dream two hours each night.
We dream more during the last four hours of an eight-hour night's sleep than the first four hours.