How does the author use foreshadowing in Requiem for a Dream: A Novel?

In Chapter Three, Sara's wonderful dream enables her to have a really happy morning. Nothing seems to be able to sour her mood until her food addiction takes hold of her. Her mind convinces her that she can't handle the diet and pushes her to panic when breakfast is over and she has to wait until lunch to eat again. In the end it is only the television that soothes her and takes her mind off of food. She is using one attachment to rid herself of another, but they each take her further from enjoying the life she has in front of her.

This segment is constructed with imagery in order for the reader to enter Harry and Marion's world. There is so much going on in the world around them as they rest comfortably in one another's arms. The scene follows closely behind Sara's, only once she wakes up she still has to face her reality even partially. This scene may foreshadow the same wake-up to reality for Marion and Harry eventually. The author chooses the word "oblivious" for their separation from reality; giving the impression that they are not purposely blocking out the real world, they are completely unaware that it is there.