I think we clearly suffer from a limbic system dysfunction, most likely a dopaminergic pathways dysfunction.
However this article focuses on inflammation and oxidative stress, but I can't see that as what we have in POIS; everyone suffers from inflammation and oxidative stress in this day and age but extremely few get POIS specifically. Thus I think we need to dig in into equally rare reasons for our POIS but also simple ones; as many theories here tackle issues that cause POIS indirectly rather than directly.