Maybe once a week or less, most of the time. It's come up several times, today, though. Part of it is that coworkers bring up the subject rather frequently. Part of it is that I have a morbid sense of humor. There's something about the process of death and decay that makes a mockery of the pride of mankind. There's something about human mortality that thumbs its nose at all wealth, being an unsolvable problem to absolutely everyone. All striving and all accomplishments are so futile for a fallen world that has no hope of salvation. They spend all day doing nothing for no one for no reason, and then they die and are forgotten. If it weren't so pathetic it would be hilarious.
As for the experience of death, I don't know. Hypoxia is not something I'm looking forward to. I've been at the death bed of a Christian, who cried in terror at the prospect of death, which came only hours later. Regardless of the unknowable that comes one second after death, I have to say that those seconds just before death leave me shaken. Whatever we can say about God's guidance and protection, he leads everyone to utter physical ruin, eventually. All we have to cling to is a trust in what lies just beyond death, in a state that can best be described as a wild guess. We trust in God that it will be something positive. We don't really know what it is; we only know that God said that it's quite nice.