Why is Gilgamesh so afraid of death?

I think that Gilgamesh really fears the unknown. He fears the lack of control that death brings.

"I am going to die!—am I not like Enkidu?!
Deep sadness penetrates my core,
I fear death, and now roam the wilderness—
I will set out to the region of Utanapishtim, son of Ubartutu, and will go with utmost dispatch!"