‘Health’ is rarely defined exclusively in terms of well-being, WHO’s (1948) classical definition is an exception. Well-being is often regarded as one of several components of the concept, however. In this view, a person’s level of health is, in part, conceptually dependent on their level of well-being. Or alternatively put, some improvements in subjective wellbeing are also, by definition, improvements in health.
This should not be taken to imply that every improvement in well-being is also an improvement in health. If a person becomes happier as a result of winning the lottery or meeting a new partner, this has nothing to do with health. Just as in the functional realm, we need to know what feelings are health related. In my view, a pleasant or unpleasant mental state is health related if it is, to a considerable extent, internally caused, and associated with the ability to perform.
This is a tricky issue, however, since a person’s hedonic level is typically caused by both internal and external factors. Anyone can be happy under optimal circumstances, which suggests that circumstances should be normal (whatever that means). We should also remember that some people put themselves in positions that would make everyone suffer. In this case, however, the problem is really functional.