Good question. First, let's get our terms straight:
Dukkha is not "suffering", it is the painful feeling of wrongness, experienced at the time of trouble, but also when craving for unsatisfied expectations, as well as mulling over inevitable looming dangers.
Sukha is not "happiness" (as in a joyful rapturous feeling we experience having attained a difficult goal), rather it is a quiet feeling of ease and comfort we experience when our existence is not burdened by troubles and emergencies.
At first approximation, when Third Noble Truth promises cessation of
dukkha, it hints at attainment of everlasting
sukha. Indeed, once you drop your attachments (as per Second Noble Truth), including positive ones (desires, expectations) as well as negative ones (aversions, clinging to something inevitably transient etc.) then the feeling of wrongness is no longer generated. In effect, all experience becomes agreeable, resulting in a permanent experience of
If we look deeper though, we can notice Buddha's emphasis on Three Marks of Existence: Impermanence, Corelessness and Dukkha as universal unconditional characteristics of existence-at-large. Because things are transient and lack a stable absolute point of reference, Dukkha is inevitably generated as mind in its modeling activity always lags behind reality. So even someone who fully understood the mechanism of
dukkha, is never 100% free from occasional experiences of "wrongness", as fluctuations of mind over long time invariably generate mismatches between "is" and "should". So in all truth Nibbana is not and can't be a sterile ease, but rather a philosophical appreciation of things as they are (
tathata) in all their complexity. Instead of being everlasting
sukha Nibbana goes beyond
sukha/dukkha by transcending the dichotomy altogether.
This understanding is reflected in the succession of
jhana stages in which the practitioner
sukha tinted with rapture, born of withdrawal from attachments and therefore from
dukkha, with help of discursive thinking.
sukha tinted with rapture, born of unification of mind (lack of inner conflict), directly with no help of discursive thinking.
- establishes and maintains
sukha not tinted with rapture, born of equanimity (seeing things as they are with no segregation into agreeable/disagreeable)
- goes beyond
sukha and indeed beyond dichotomy of sukha and dukkha, resulting in pure nonjudgmental awareness.
To summarize, Buddhist practice initially focuses on reducing and ceasing
dukkha, then on generating
sukha, and finally on transcending
To answer your question directly, because experience of
sukha relies on "what is" matching "what should be", (just like experience of
dukkha relies on the two mismatching) it still belongs in the category of conditional experience. In this sense the experience of
sukha always has a shadow of
dukkha looming over it, like you correctly supposed. Like you said, right and wrong co-imply each other, and Impermanence connects the two, guaranteeing that any "right" condition will not last forever. It is that feeling of being unable to fully enjoy vacation because of the need to return to work eventually. So your original premise is correct, by its very nature
sukha always has a seed of
dukkha in it, due to it being conditional.
Thankfully, Buddha-Dharma does not leave us at that. To build on vacation metaphor, Buddhism solves the problem of having to return to work by dissolving the essential difference between vacation and work. Nibbana-as-permanent-vacation is just a provisional motivator (
upaya) utilized on initial (Hinayana) stages, before the student progresses enough to appreciate the full-scale teaching. When our mind is fully integrated, and we always do our best, then our creative spirit is shining continuously wherever we are and whatever we do. This fully integrated (and therefore unconditional!) experience is known as
tathata and the one who realized it is called