Siebe asked: “in which sense does that bad meditation you describe differ from sannavedayitanirodha?”
There is a HUGE difference between “saññā nirodha” that I described above and “saññāvedayita nirodha” that can be experienced ONLY by an Arahant who has cultivated ALL jhanas too.
– P.S. To get to saññāvedayita nirodha” an Arahant has to systematically go up through all the jhanas, and then get to saññāvedayita nirodha.” That is, in essence, the full experience of Nibbana. He/she can stay in that state for up to seven days.
– P.P.S In other words, in “saññā nirodha” thoughts arise without much of past memories. In saññāvedayita nirodha” thoughts DO NOT arise (like in full Nibbana after the death of an Arahant.)
See (starting from #12) in the post, “Nirōdha Samāpatti, Phala Samāpatti, Jhāna, and Jhāna Samāpatti“