it also deppends on which method was used or what caused death.
for example substances that interact with gaba like N or benzos may give you an entire diffent death "experience" (if there even is one) from substances like SN or opiates.
this is a very interesting subject since there is not much research on it, i assume it is very difficult to know exactly what is happening inside the brain of someone already clinically dead and it is not exactly ethical to conduct such researches or experiments.
maybe @Underscore is right and our perception of time is greatly dilated. this will explain exactly where our concept of afterlife comes from, we will never know until it happens.