A fundamental suffering related to feelings of nihilism?
Dukkha is usually translated as suffering, which sort of works but misses important stuff. A more literal translation is 'a difficult emptiness.' Approaches, even quite effective ones, for dealing with the suffering of life were already in existence at the time of the Buddha. Both schools that preached constant absorption into pleasurable meditative states, and schools that preached a doctrine and practice of 'non-duality.' Both of these approaches survived, became mixed up with Buddhism, and today there are schools claiming to teach Buddhism which actually teach these methods. These methods do in fact decrease suffering, but they are only partial solutions. Both because they are reliant on maintenance of certain states and ways of being, and because while they deal with suffering caused by the immediate senses, you are still left with a more fundamental suffering related to feelings of emptiness or, Dukkha's other translation, 'worthlessness' and related feelings (nihilism etc. in the west). You've encountered this for yourself if you've experienced something cool during contemplative practice but then had a kind of 'so-what?' moment. The sense that this experience, while interesting and probably a temporary respite from your worries, hasn't actually addressed the core problem. People especially have this coming back from retreat. If this were just considered on its own, without the teaching of the antidote, this might be called worthlessness, that it seems like things are never satisfying and thus nothing has any value.