The first paragraph is very troubling: it uses fear, anxiety, sleeplessness, and the "groaning" sound of a fog-horn in the distance. Nick wants so badly for things to be cleared for Gatsby. Gatsby is a good guy, especially compared to people like Daisy and Tom. He has dreams/nightmares and he can barely wait to jump out of bed to go see if he can help Gatsby before he gets into serious danger or trouble.
"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."