A clarification about Nirodha Samapatti: The word "nirodha" simply means "cessation". It is used with the qualifier "samapatti" to mean "The Cessation of Perception and Feeling", a very unusual accomplishment only available to very small subset of advanced meditators, those way out past Stream Entry with full access to formless realms who are at least anagamis and who can figure out how to translate those two impressive attainments into the even more impressive attainment of nirodha samapatti. The term "nirodha" is sometimes used to refer to fruitions, which are discussed in the Abhidhamma, and here is simply means "cessation". So, if there is ambiguity, it is typical to clarify what one means, but, in the discussion of stream enterers, as they are incapable of attaining to "nirodha samapatti", by convention we generally presume that "cessation" simply means "fruition" in stream enterers' cases.
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Nirodha Samapatti, it is actually by far the easiest of the various experiences to identify clearly, standing out strongly from all of the rest of them as it does:
Meditator: only anagamis and arahats with mastery of the formless realms and the ability to ride a strange line between samatha and vipassana with a high degree of balanced, tranquil, easy control can even think about attempting this, so it is already a strangely small crew. In fact, I can count on one hand the number of people that I personally know that I actually believe have attained to this. If you are not an anagami or arahat with strong technical mastery of jhana and insight, you haven't attained this, so you can remove it from your differential diagnosis. In fact, if you are asking the questions you are, it is pretty much guaranteed that you haven't attained this. The chances of most meditators attained this in their lifetime are so small that it is very rarely something to seriously consider as what might have occurred.
Setup: You rise with very light, easy effort up through the jhanas to the 8th jhana while mixing in about 30% insight. You come out, and, having resolved gently to attain to NS either when you started the rise before the 1st jhana or resolving now, you chill and do nothing. NS either happens within a minute or two or it doesn't, and most of the time it doesn't.
Entrance: Thoughts, body and consciousness itself vanish rapidly in an analogue fashion over less than a second. It is a total, dramatic power failure. This is easily distinguished from the Three Doors, as it involves none of these: rapid impermanence, something falling towards you, something falling away from you, or any other Door variant.
Thing itself: No experience, time, or anything at all. To a person watching, they appear still on their cusion or laying down or whatever posture they are in and will be hard to get to come out of it by external stimuli.
Exit: Exactly like the entrance but in reverse order, like consciousness and experience powering up again in a rapid analogue fashion. This is distinct from the restart after Fruition.
After-effects: The afterglow is heavy and powerful beyond reason and oddly long-lasting, typically lingering for 5-24+ hours, like one had taken some perfect drug that was at once highly chill but also produced a great deal of stable alertness. I think of this as what people are attempting when they mix uppers and downers, but the NS afterglow is perfect version vs what people typically get when they do that, which is at once muddled and edgy, whereas the NS afterglow feels, well, sublime, divine, incredibly right. No other attainment has an afterglow this good. It takes the top prize with no close competitors.
Fruition is also easy to identify in theory, but harder in practice, as there are lots of possible mimics, and it doesn't have the extreme marks.
Meditator: One who has at least attained to Equanimity, Conformity, Change of Lineage, and Path insight stages the first time or is at least a Stream Enterer in Review. It doesn't occur to non-noble ones. So, the entrance criteria are vastly lower than NS.
Setup: One rises through the stages of insight to Equanimity and attained to Confromity Knowledge. So, one requires much less meditative skill and technical competence than for NS.
Entrance: Through one of the Three Doors, as describe in MCTB2. These are all quite different from the entrance to NS, which is analogue and doesn't involve the rapid presentation of the Three Characteristics in the same way as the Three Doors do.
Thing itself: Again, like NS, there is no time, space, consciousness, etc. To a person viewing them, they typically have their eyelids blink and then come out of it clear and seemingly normal if it last a very short time, or, if it lasts longer, they would view them as a still mediator on their cushion without obvious response to the outside world. So, externally, during Fruition that has duration to it or NS, the meditator will appear largely the same, though their breathing may be much slower in NS.
Exit: The mind restarts very rapidly clear and clean, fresh, bright, present, satisfied, like it has been reset and refreshed.
After-effects: This bright, clear, refreshed feeling typically lasts seconds to minutes and then fades rapidly, the major exception being the first time a path, particularly stream entry, is attained, after which the after-effects can be more dramatic and longer-lasting, but are nothing like the NS afterglow, which stands out as its own thing.
dDx (medical abbreviation for "differential diagnosis", meaning things that could mimic Fruition): a momentary blip into a formless experience, any state shift between one state or stage and another, the A&P, Dissolution, and some others. It is very, very common for people to think they have attained to a Fruition when, in fact, they have not. Probably 98% of people I talk with who are trying to determine if they have them don't at all meet the criteria, IMNHO. It is true that plenty of people are relatively poor phenomenologists, making sorting this out difficult, but it is still worth attempting.
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