House told Joy she was pregnant and this explained both her nausea and rash. However, Joy insisted she wasn't pregnant. House asked if she had ever had sex and when she said she had, he insisted she was pregnant. He also pointed out that it was obvious her breasts had become bigger recently as her bra was too small.
However, when Cuddy started to exhibit the same symptoms, House had to come up with a new diagnosis. After improvising a lumbar puncture on Peng and ruling out meningitis, he told the plane that the disease would cause a shaking left hand. After several people, including Joy, started having shaking in the left hand, he realized everyone but Peng was suffering from conversion disorder. Once he reassured everyone, Joy started feeling better.