The following post is from C. Saket:
Asanna state is like a coma, unconscious, lifeless, no citta…
An Asanna Brahma has all the asavas remaining, hidden. Whereas Nibbana is attained by permanently removing all the defilements, asavas.
However technically speaking, in both cases of “Asanna” state and “Nirodha Samapatti”, sanna and vedana are absent.
But that is the only similarity between the two.
There is a huge difference between an Asanna Brahma and the state of Arahant after death (Parinibbana).
Parnibbana is nothing like Asanna. It cannot be described by using rupa, citta and cetasikas at all !!! It is beyond this world!!!
To illustrate this error of regarding Nibbana as sheer nothingness, some Buddhist monks relate the story of the turtle and the fish. There was once a turtle who lived in a lake with a group of fish. One day
the turtle went for a walk on dry land. He was away from the lake for a few weeks. When he returned he met some of the fish. The fish asked him, “Mister turtle, hello! How are you? We have not seen you
for a few weeks. Where have you been? The turtle said, “I was up on the land, I have been spending some time on dry land.” The fish were a little puzzled and they said, “Up on dry land? What are you
talking about? What is this dry land? Is it wet?” The turtle said “No, it is not,” “Is it cool and refreshing?” “No, it is not”, “Does it have waves and ripples?” “No, it does not have waves and ripples.” “Can you
swim in it?” “No you can’t” So the fish said, “it is not wet, it is not cool, there are no waves, you can’t swim in it. So this dry land of yours must be completely non-existent, just an imaginary thing, nothing
real at all.” The turtle said that “Well, may be so” and he left the fish and went for another walk on dry land.
In the Asaṅkhata Saṁyutta (SN 43) Lord Buddha uses various synonyms for Nibbana:
This clearly shows that Nibbana is nothing like Asanna.
Nibbana exists as an UNCONDITIONAL ELEMENT and it is beyond all our experiences of this world of 31 realms.