Why we know stuff out of nowhere?

Why is it that when we are in a dream we know for sure what to do even if no one told us or it never happened before? I'll explain:
In today's dream i was on the street going to the place where an old colleague of mine was having a birthday party. Why did this came to my mind? I say this because this colleague of mine was not a person that i knew very well and she left work some years ago.
Other situation: once i dreamt i was on a different country and saw a woman that i knew to be my wife. Why did i know this? I'm not married. I don't even have a girlfriend.

Sometimes i'm in a dream and i know exactly what to do or take the current situations as normal, even if it never happened in real life.
Does this happen to you? Why we know this stuff out of nowhere? It looks like this "stories" were planted on our minds when we sleep.

I know exactly what you mean. The best answer I can give is that the subconcious mind is weird.

I believe this to be a very normal phenomenen as i have experienced it many times myself. When i dream i often feel "auras" of people and their attitude, something i do not do in real life. How and why this happends remains unclear, but it does not surprise me that it does. Think about it, when you dream all the information comes internally, what kind of information this is must vary a lot. So when the brain builds a dream enviroment it adds information like that to the piece. This is what i suggest atleast.

It's pretty normal, in dream our memory often happen to be different. It can be based on various things, something that you heard or were thinking about at some point, or something that is based on stories that you read somewhere, or on something that you watched, and so on. It is even possible to be completely different person or being in dream. :P

Well hello! :-) I've always found these false dream memories fascinating. I remeber one where I had a brother who I was very close to. When I awoke, I realized that no such brother existed!

Perhaps these "memories" we have in dreams reinforces the "seeing is believing" idea, which can be important to survival. Like when a suicidal animal owner in Ohio, US released tigers, lions and other exotic animals to roam nearby residential areas. Safer to accept there's a tiger is walking up the street than to question reality. It's like dreams are always trying to get us to accept a situation no matter how odd. Hope I made some sense :-)

On a side note, there was news some time ago that ads can make people believe they've eaten food that they'd never actually tried: Ads Implant False Memories - Wired Science Makes you wanna keep a daily journal of your waking life too!

The subconscious supplies you with all you need to know about its story.

This happens if you take deliriant drugs too. You will begin to think you are in another place, in completely different circumstances, it's like being in a dream... but awake. Not like a lucid dream either, but literally just becoming delirious. This has always led me to believe that dreaming is a form of delirium. I guess by definition, it kind of has to be. You believe things that are not true, you see and hear things that are not there, and you are unable to logically reason.

I would like to throw in the idea of past life issues. I feel that experiences that are somewhere ina locked away part of your spirit can leak through into dreams.

All good ideas, guys; can I add a sort of boring, mundane reason? When you are dreaming, your memory is shut off.

It's that simple. When your dreaming mind creates its scenarios, it tends to supply images, plots, and "historical" information in a fairly random (or deeply cryptic, for the dream interpreters out there) and piecemeal way, and at the same time you are unable to access your memory and understand that all this stuff is wrong.

So when dreaming you are unable to remember where you were five minutes ago, much less that the relatives you're talking to have been dead for ten years, or that the house you're in has nothing to do with yours, even though in the dream you are sure it's yours. It's all about memory, guys, which is why "restarting" memory is so important during LD's.

Well, mostly about memory; though I understand the reasons for accepting strangeness, I still have some issues about certain dream characters, plots, or locales that defy anything in my experience, and continue to defy even after I'm fully lucid and I remember.

It's difficult to pin down, but I think theories like LaBerge's "schemas" work well most of the time, and add to that a lack of memory....then you have a new life.

Then there are those dreams in which interpretation actually works, and in such a way that there is no doubt of the message. These are less frequent, and do not usually feel like the result of simple associations.

Finally more rare are those unexplainable dreams, such as the ones that come true to a certain degree; among other strange things, but I digress.

I do love this field of exploration.