Johnny Lim said, “Which implies that on the attainment of 2nd jhana, 4th jhana, and Nirodha Samāpatti, vaci sankhara, kaya sankhara, and citta (mano) sankhara stops, respectively. Emergence from Nirodha Samāpatti is just the reverse order..”
That statement should read, “Which implies that on the attainment of 2nd jhana samapatti, 4th jhana samapatti, and Nirodha Samāpatti, vaci sankhara, kaya sankhara, and citta (mano) sankhara stops, respectively. Emergence from Nirodha Samāpatti is just the reverse order.
It is important to understand the difference between jhana and samapatti. Vaci sankhara are not stopped in the second jhana, but is stopped in the second jhana samapatti. Similarly, kaya sankhara are stopped only in the fourth jhana samapatti; that also means breathing is also stopped in the fourth jhana samapatti.
All thoughts cease to exist in nirodha samapatti, i.e., no mano sankhara. The only difference between one in nirodha samapatti and a dead body is that dead body is decaying and body temperature drops. When one is in nirodha samapatti, body temperature drops some but remains at that level; life is maintained by kammic energy.
When in a jhana, jhana citta vithi do not run continuously; there are citta vithi corresponding to pancadvara running in between jhana citta vithi. That is why one in a jhana can hear, see, etc.So, one does generate all three types of sankhara when one is in a jhana.
But when one is in a jhana samapatti, monodvara jhana javana citta run continuously. Therefore, one does not hear, see, etc while in any jhana samapatti, as well as in nirodha samapatti.
The basic ideas and a bit about jhana samapatti are discussed in the post: “Citta Vithi – Processing of Sense Inputs“.
In addition, only vaci sankhara are stopped in the second jhana samapatti. Only vaci and kaya sankhara are stopped in the fourth jhana samapatti. All three are stopped in the nirodha samapatti.