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.