Let's see, how can you prepare? I would repeatedly tell yourself in the days leading up to the experience how everything will end up ok, and that the experience will wear off within a few minutes. The reason why it's necessary to repeat this to yourself is a matter of conditioning. You want to make sure that when you are in the throws of a hyperslap, that instead of panicking, the first thought to reflexively come to mind is that "everything will be over within a few minutes."
DMT can play off your emotions as if it had a remote control for it; so if they hit the panic button, that will be the syndrome of emotions and physiological reactions that will immediately ensue. The thing about panic or fear is that it has two sides to it. One side is physiological, and this cannot be avoided so much. The other side of it is rational. These are logical reasons for being afraid of something. In everyday life, these two tend to go hand in hand, but they don't necessarily have to. In hyperspace, there will be times when your body will be telling you that you're afraid, but if you can remind yourself how it will all be over soon, and there isn't much to fear, then you can keep calm, and this can help shift the physiological reaction as well. Since panic can cloud your thinking, you need the thoughts to be reflexive.
In martial arts, they teach you how to fall. When you get into a car crash, there are more appropriate ways than others to promote your safety. You essentially want to "rag doll" allowing your muscles to go limp. This will minimize the damage even though your instinctive, reflexive reaction will be to tense up. So how do martial arts teachers get you to circumvent that reflex? They condition you, just like you want to condition your thoughts. If you're getting hyperslapped around, the best thing to do is take on that kind of persona that is useful in the dentist chair: "Yes this is uncomfortable. Yes this hurts. It's only just a little bit longer..."
Ultimately it is possible to thoroughly explore the heavens of hyperspace without much of a glimpse at hell...but it's like gambling; the more you do it, the more likely you are to eventually lose, but there can still be that guy who wins the jackpot on beginners luck, makes his fortune and decides to never gamble ever again, having gotten what he came for.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb