There is research on the links between downward social mobility and happiness, however:
These empirical studies show little consensus when it comes to the consequences of intergenerational social mobility for SWB: while some authors suggest that upward mobility is beneficial for SWB (e.g. Nikolaev and Burns, 2014), others find no such relationship (e.g. Zang and de Graaf, 2016; Zhao et al., 2017). In a similar vein, some researchers suggest that downward mobility is negatively associated with SWB (e.g. Nikolaev and Burns, 2014), while others do not (e.g. Zang and de Graaf, 2016; Zhao et al., 2017)
This paper suggests that differences in culture may influence the connection between downward social mobility and happiness:
the United States is an archetypical example of a success-oriented society in which great emphasis is placed on individual accomplishments and achievement (Spence, 1985). The Scandinavian countries are characterized by more egalitarian values (Schwartz, 2006; Triandis, 1996, Triandis and Gelfand, 1998; see also Nelson and Shavitt, 1992)...A great cultural salience of success and achievement may make occupational success or failure more important markers for people’s SWB.
And they claim to find this:
In line with a previous study from Nikolaev and Burns (2014) we found that downward social mobility is indeed associated with lower SWB in the United States. This finding provides evidence for the “falling from grace hypothesis” which predicts that downward social mobility is harmful for people’s well-being. However, in Scandinavian Europe, no association between downward social mobility and SWB was found. This confirms our macro-level contextual hypothesis for downward social mobility: downward social mobility has greater consequences in the United States than in the Scandinavian countries.
This is, of course, just one study so not very conclusive.