dreams are??

There is allot of people in the world who believe that dreams are sign, especially in the past people thought of it as a superstition. As I read the tablets of Gilgamesh I thought as they talked about the dreams they had and how it represent the creature that they are going to encounter I imagined that this being and old text people at that time imagined dreams as a sing. But then a dream according to a doctor is a recompilation of the things that happened on your day. So I think how it that people thought of dreams as a sign. But then it made it clear that once again “on the next day they travelled fifty leagues, and fifty leagues a day for two days more” (pg 22) this text is in the past and they believed that a white bird was sign of peace and etc. In my opinion people had no way on knowing things like the anatomy of the body since they don’t have the technology that we do right now.
Gilgamesh is one of the oldest texts we have of the world so in represents what the people believed in so we have to trust the people of that time. Who are we to trust? How can we believe if it is really sign?