Tom started to panic because he looked down and suddenly realized how dangerous his situation really was. Jack Finney describes in great detail how Tom pursued the yellow piece of paper out of the window, lowered himself carefully towards it, and was finally able to clasp the corner of the paper in his fingers. Up until this point, Tom was focused on the recovery of the paper to the exclusion of all else, including fear. At this point, however, looking down at the paper caused him to look further down, to Lexington Avenue; far, far below:

He saw, in that instant, the Loew's theater sign, blocks ahead past Fiftieth Street; the miles of traffic signals, all green now; the lights of cars and street lamps; countless neon signs; and the moving black dots of people. And a violent instantaneous explosion of absolute terror roared through him.

It is at this point that the story of Tom's ordeal truly begins. The recovery of the piece of paper, though it seemed important to Tom when he went out of the window, was a trivial matter. Now, he is engaged in a frantic struggle for his life, and his mind, instead of doing all it can to ensure his survival, is morbidly focused on distracting and distressing him by imagining the aftermath of his death. The panic Tom feels upon looking down, however little it helps him at that moment, is the beginning of his struggle for survival, and the reassessment of priorities that is its result when he does manage to survive.