why does gene get upset when leper describes his hallucinations?

Leper reveals that he imagined Brinker's head on a woman's body, people's faces would take on the characteristics of people he'd known before, he couldn't sleep in the barracks, and he couldn't eat in the mess hall. This is pretty upsetting imagery. Gene laments Leper’s drastic change from a curious empathetic boy to a disturbed and broken young man.