How is Holden’s physical condition deteriorating in this chapter?

Every time he steps down off the curb to pass over a road, he thinks he may just keep falling and evaporate. He asks his dead brother, Allie, to help him. Holden is physically and emotionally debilitated, sweating profusely despite the cold. He is near collapse. Holden’s anxiety as he crosses streets on Fifth Avenue is reminiscent of the feelings that he had on his way to Mr. Spencer’s home near the end of Chapter 1. There, too, he felt that he was disappearing every time he crossed a road. The terror is related to the horror he feels toward mutability and death.