Other than the fact that Holden must have depression and anxiety issues, he has a traumatic past. At age 13, Holden loses his 11 year-old brother Allie to leukemia. And this wasn't just a loss of a sibling, but he really loved and respected his little brother. Holden loves his deceased brother so much that he keeps his brother's baseball mitt with him at school. He also uses the poetry written on it as inspiration. How he describes his brother, though, shows a loving connection to him as well as a deep sense of loss that probably haven't been properly dealt with three years after the fact.
"He was two years younger than I was, but he was about fifty times as intelligent. . . But it wasn't just that he was the most intelligent member in the family. He was also the nicest, in lots of ways. He never got mad at anybody. People with red hair are supposed to get mad very easily, but Allie never did, and he had very red hair" (38).
Not only did he lose the nicest person in his family, but one might infer from this quote that maybe Holden doesn't think his parents are nice people. And since Holden seems to get kicked out of preparatory schools over and over again, he might be holding a grudge against his parents for sending him away from home. Feelings of rejection and loss of a loved one can certainly bring a person down and feeling negative.