This technique wasn't made as a way to relax. This is what the technique is for: The Death Posture is an intense, physically exhausting technique that uses the link between mind and body to deeply imprint personal goals onto the mind. By straining the body to its limits, the mind is moved to a state of "gnosis" that acts as a doorway to the unconscious, making any visualizations or affirmations done using this method extremely powerful. It is not a beginner's method, but it is extremely effective when used properly.
The method itself can aid with astral projection and entering a trance/trance-like state. I would highly suggest attempting those only after you complete the exercise to the point of exaustion described, as that is when your body would be entering the "Gnosis" state described. But make certain that your body is strong enough to handle this posture, as it will cause discomfort either way. The purpose of the exercise is to push your body to a state of exaustion and strain, which will then trigger a different state of consiousness,"Gnosis",which in a sense, would be a trance. Just make certain that you know your limits, because this pose isn't for beginners.