Gilgamesh has several dreams in the story. The first is of a giant boulder that threatens to crush the earth. Gilgamesh rushes to catch the stone, & when he embraces it, it turns into flesh. Ninsun interprets this as Gilgamesh meeting his equal. He of course will come in the form of Enkidu.
However, Gilgamesh also has terrible nightmares on the way to kill Humbaba. They all involve defeat of some sort, usually ending with Gilgamesh and Enkidu being crushed or somehow killed. However, Enkidu twists the meaning of each, somehow interpreting them to mean that Gilgamesh and Enkidu will successfully defeat Humbaba. This they do, but they also suffer greatly for it.