This is often a kind of personality related question. When you think about being super afraid at the moment of death, say the earthquake that was mentioned before and so on, what you've trained your mind to do may come up. If you haven't trained your mind, then you just stay in the fear, so when I say train your mind, I'm talking about mental development. If you've done lots and lots of Compassion/Lovingkindness meditation, you've trained your mind to bring it up more automatically. Then at the moment of death when you see some fear, you might go ,"Oh, wait a minute, not fear, I'll do some Compassion/Lovingkindness, I'll do Compassion/Lovingkindness for everyone as I'm dying."
Now you are looking at one person who is very strong at that practice, and it does come up for me automatically. And it has come up for me automatically in supposed nightmares where I'm supposed to die. Not only once, but even in one nightmare it was a double death. I'm in a car, a truck it seemed to be, and it's going off a cliff, it's going down, that's it. I realize that I am going to die and I start doing Compassion/Lovingkindness for the whole world, knowing I am going to die. In that particular dream, the truck hit the water and we go under it, we're drowning then, I haven't died yet. I do it again, realizing that I am going to drown. For me it was automatic, it is trained so that it comes up automatically in times that should be fearful--scream, yell, wake up from a nightmare and so on. It's happened many times for me.
Now, I've got a friend who has experiences that are similar, not just in nightmares but in real life, of fainting, and being very sick, weak and fainting, and then reflecting on the Buddha, Dhamma, Sangha, because that's one of their favorite reflection meditations. It has come up for them many times, the same reflection comes in that moment when they think they might be dying. It totally takes away fear. It is gone. Because the person has trained it, over and over and over. So, look to your own personality, find one of the very nicest reflections that you like, and make sure it is a solid one, keep it going, bring it up over and over, make it solid. Love it, hug it, protect it, keep it and whatever. And then it may come up automatically in a moment of fear, so that you can die more peacefully, connected with the Dhamma in some way, and hopefully get a good rebirth.