Wow, that's an amazing question I don't have an answer to.. but, purely speculating here, SN acts by the formation of methemoglobin, meaning that O2 is reduced in the blood, meaning that the brain is slowly starved of oxygen. As far as I know, SN does not affect brain chemistry directly, but only acts through this particular mechanism of oxygen deprivation of brain and body. In that scenario, I would assume that you CAN get the release of DMT and all the other chemicals that lead to NDEs and the associated feelings described. (NDE are not reliably triggered, we cannot know how many people experience death as pleasurable or peaceful.)
With N I'm very unsure, it causes death by respiratory depression which also leads to oxygen deprivation of the brain. BUT N is also a known CNS depressant, used to induce sleep in for example anesthesia. As fas as I can gage from online sources, dreams have not been reported with pentobarbital anesthesia. So it is possible that with N you are just 'out'.