In what chapter does this book show evidence of Ishmael Beah isolating himself?

There are many chapters that Ishmael will isolate himself. There are different situations.

One is in chapter 16, Ishmael will isolate himself because he is going through withdrawal after not having cocaine, brown-brown (mixture of cocaine and gunpowder that is inhaled through the nose), and marijuana. During the night Ishmael often woke up from nightmares and had very aggressive reactions. There were an assortment of reactions that many of the boys had, included punching the air wildly and choking the person that was sleeping next to them. Once in chapter 16, Ishmael woke up from a nightmare he was having where he was having his neck sliced by a bayonet, much like what had occured when he was named junior-lieutenant. After waking up he started punching the air aggressively. When he had calmed down from that, he ran out to an open area in the rehabilitation center (Benin Home) and sat and rocked back and forth while crying.

There are many more times in the book that you will find Ishmael isolating himself. Often happening after a death of one of his family members or friends or a traumatizing experience that he had been involved in or seen.