What were nature of Nicks Dreams during that night? Gatsby is standing on the steps of his house, waving goodbye. Where have we seen this motif before? What did it evoke then? now?

From the text:

"I couldn’t sleep all night; a fog-horn was groaning incessantly on the Sound, and I tossed half-sick between grotesque reality and savage, frightening dreams. Toward dawn I heard a taxi go up Gatsby’s drive, and immediately I jumped out of bed and began to dress — I felt that I had something to tell him, something to warn him about, and morning would be too late."

We saw this motif at the very beginning of the novel when Gatsby was looking out over the water from his lawn.