Dreams are funny things. While you sleep its the brains unconscious way of telling you what you want, yet you didn't know that, because you didn't even know what you wanted.
There are also other types of dreams, people call them premonitions, its when you dream of something with explicit details and that same thing happens outside of that dream, in the real world. Its more than just dreaming of something that is obviously going to happen, like a plane crash, a plane crash can't be called a premonition, because it is obvious that a plane will crash someday in the future. No, premonitions are more specific, they contain too many details to be called "coincidences".
The dreams Gilgamesh had, are another kind of dreams, in those types of dreams people and certain actions are represented by inanimate objects and some kind of disasters (may be natural or even man made) or even miracles. Dreams like that can leave a heavy conscious on anybody, yet Enkidu reassured him every time that all those dreams he had were of good luck, that they should keep on their way to the Cedar Forest. In the end it appears that Enkidu was right all along, Gilgamesh was able to defeat Huwawa and cut his head to take back with him to Uruk, along with gates he built for his city with the cedars found in the forest. With a raft he built together with Enkidu he started his journey back to Uruk.
