In a word, this article advises: Don’t fake it (being happy that is). Which, umm, I don’t think we needed a study to prove.
“The scientists examined what happened when the drivers engaged in fake smiling, known as “surface acting,” and its opposite, “deep acting,” where they generated authentic smiles through positive thoughts, said an author of the study, Brent Scott, an assistant professor of management at Michigan State University.
After following the drivers closely, the researchers found that on days when the smiles were forced, the subjects’ moods deteriorated and they tended to withdraw from work. Trying to suppress negative thoughts, it turns out, may have made those thoughts even more persistent.”