Nothingness, albeit with a caveat.
I think that our brain basically defaults to a dream where we see generally what we feel, assuming the brain isn't in a critical condition where it can't function. It could be a vision of heaven, hell, and old memory, family members, and so on.
My general reasons for saying this is based around a couple things.
NDE(near death experiences) that have been documented generally have themes lights, tunnels, relatives, and any amount of cultural expectations. For instance, a Muslim might see what they expect of Jannah, a Buddhist might see the start of their rebirth, or a Christian might see heaven.
Additionally, the brain starts going crazy before death. There have been a decent amount of studies on humans and a good amount of studies on rats which show that pre death, the brain on an EEG shows surges of high frequency gamma activity in areas that are activated during dreaming and memory recall.
As such I generally believe that we simply enter a dream like state, before the brain shuts down entirely and functioning ceases all together. At that point I imagine it's like how it was before we were born.
But this is just my personal hypothesis and interpretation. I don't wanna step on anyone's religious beliefs <3. In the end nobody knows what happens after death. Make of it what makes you feel best.
