My Facebook friend, Duff (he blogs at Beyond Growth), shared a link to this article a few days ago. It may seem like it's from The Onion, but it is legitimate, cited in PubMed and everything. If it weren't so accurate, it would be a lot more funny.
It is proposed that happiness be classified as a psychiatric disorder and be included in future editions of the major diagnostic manuals under the new name: major affective disorder, pleasant type. In a review of the relevant literature it is shown that happiness is statistically abnormal, consists of a discrete cluster of symptoms, is associated with a range of cognitive abnormalities, and probably reflects the abnormal functioning of the central nervous system. One possible objection to this proposal remains - that happiness is not negatively valued. However, this objection is dismissed as scientifically irrelevant.
Citation:Bentall, R.P. (1992). A proposal to classify happiness as a psychiatric disorder. Journal of medical ethics, 18; 94-98.