Niramisa sukha is at different levels.
– Niramisa sukha of an Anagami is higher than that of a Sotapanna, for example.
– Once one has a magga phala, niramisa sukha corresponding to that stage WILL NOT decrease.
An average human may have niramisa sukha, too, when living a moral life.
– But, that can decrease if that person gradually moves to an immoral lifestyle. Normally that happens under the influence of “bad friends” (“bad influences.”)
That is why the eight levels of magga phala (Sotapanna Anugami to Arahant) are special. Once understanding sets in at a certain level, it (and the corresponding niramisa sukha) will NEVER go away.
Please keep in mind that it is better not to open too many new threads. You could have asked this question in the old thread.