What is the scientific explanation for dreams?

Is there any explanation on why do people have strange dreams during the same time period?

• EDIT: I've rephrased this question here: An example: At least 10 of my friends, and myself, have been dreaming vividly during the past two days. I'm not trying to understand if there is a reason for this particular event, but any event in which people might experience vivid dreams during the same time. Since we only remember 10% of the dreams we have dreamt, (seehttp://science.howstuffworks.com/life/inside-the-mind/human-brain/dream4.htm) the probability of someone remembering a nightmare or a weird dream is lower than this. So having 10 or more people remembering vivid or strange dreams in two days in a row is curious. Is there any good explanation for this? - The only common denominator is that we are all living in Stockholm (if that is relevant). Most of us haven't done any similar activities together (except a couple of colleagues). We are all adults in our mid or late 20s. Some extra context: I found out about this when I mentioned to one of my friends that I have had a nightmare, and he told me that he had one too. Then 2 more overheard us and mentioned that they have been having weird dreams as well. Finally I asked on Facebook and other people that live in my city answered affirmatively.

• Answer:

  Confirmation bias and a lack of understanding of probability.