From Scientific American:
Norman Cousins, the storied journalist, author and editor, found no pain reliever better than clips of the Marx Brothers. For years, Cousins suffered from inflammatory arthritis, and he swore that 10 minutes of uproarious laughing at the hilarious team bought him two hours of pain-free sleep. In his book Anatomy of an Illness as Perceived by the Patient (W. W. Norton, 1979), Cousins described his self-prescribed laughing cure, which seemed to ameliorate his inflammation as well as his pain. He eventually was able to return to work, landing a job as an adjunct professor at the School of Medicine at the University of California, Los Angeles, where he investigated the effects of emotions on biological states and health. The community of patients inspired by such miracle treatments believes not only that humor is psychologically beneficial but that it actually cures disease. In reality, only a smattering of scientific evidence exists to support the latter idea—but laughter and humor do seem to have significant effects on the psyche, even influencing our perception of pain. What is more, psychological well-being has an impact on overall wellness, including our risk of disease.
Laughter relaxes us and improves our mood, and hearing jokes may ease anxiety. Amusement’s ability to counteract physical agony is well documented, and as Cousins’s experience suggests, humor’s analgesic effect lasts after the smile has faded. Cheerfulness, a trait that makes people respond more readily to laugh lines, is linked to emotional resilience—the ability to keep a level head in difficult circumstances—and to close relationships, studies show. Science also indicates that a sense of humor is sexy; women are attracted to men who have one. Thus, in various ways, life satisfaction may increase with the ability to laugh.