Could The Tibetan Book of the Dead be something that can possibly help to further explain the hyperspace, mystical experiences and life/death cycle?
If we take it as possibility that what is described in the texts as something that has valid information/description of parts of after life then i will go and flex my imagination and include some of my personal experiences from entheogen induced mystical states and say: Are we by exploring this actually making our ˝souls˝ more prepared for the things that will transpire at the moment of our death and there after?

I'm already prepared. So it could be. If someone told me "you're gonna die tomorrow", I'd just accept it and say "well, if it must be so...".

So, death anxiety is now minimal in my case. What I'm anxious about is inevitable death of my loved ones. It's more fear of separation than anything else. I believe they will return to "those realms", but I don't want anyone to take them away from me.

If stretching is nothing comparable to running, it sure makes the running smoother.
But only if the stretching was done properly!
Wrongly stretching can cause issues by itself, compromising the running afterwards.
So it's ambiguous.

Taken this to the "Tibetan Book of the Dead" attitude :
there, death, is promoted as an opportunity to melting in the "unifying", to break karmic cycling.
Our experiences can stretch us in favor for this unifying-event, but can also hinder that.
The difference lies in the attained ability of letting go of "clinging onto phenomena".
The psychedelic experiences are huge phenomena, so good exercises.

Is how I understood and connect our practices to "The Book" theory.

Loosing own fear of death but not fear of loosing others...infinite shades of fear.
I have my own mix that is giving me rest and at the same time keeping me restless.
I feel you oversoul.

So the trick is to keep things in moderation ...including the moderation itself.
Funny that until we actually have real death experience we can't be sure of anything even after all my experiences that left me with almost 100% certainty there is that 0,00001% of unknown and doubtful creeping in shadows of my own mind that overtakes as time passes by while i integrate some of those deep voyages until i have another experience that resets me back again.

I believe so, but it may be important to keep various theories about hyperspace in mind. If it is an inherent part of the universe or multiverse in which we reside, then The Tibetan Book of the Dead offers little more than the ancients' interpretation of their explorations of this place.

Final end-all be-all answers are rare if they even exist, which is why we must construct theories surrounding our experiences. I have read Leary's version (The Psychedelic Experience) only, but from the Bardos he described, I think there are definitely parallels to psychedelic journeys, including DMT trips.

As for preparation for death, I think that most psychedelics severely reduce the anxiety surrounding our departure, possibly because of a severing of our egotistical ties to this plane. For some people this is a positive thing, but for others they might prefer to hold onto the physical world that surrounds them. It seems that if you want to start letting go of this world and exploring what could possibly come next, psychedelics and Bardo exploration is the way to go.

Read "Mirror of Mindfulness" by Tsele Natsok Rangdrol The subtitle is "The Cycle of tho Four Bardos" It explains more clearly than the Tibetan Book of the Dead about the bardo thodol. In it, death is explained to happen in stages, when your body is no longer functioning (physical death), then is the opportunity to experience enlightenment. Most people are so filled with fear that they go "unconscious". MoM explains in great detail with practice instructions, up to re- birth. There are hyperspace moments that seem like what all of the stages may be like.

There is a guide to Chogyam Trungpa's Tibetan Book of the Dead written by his co-author Francesca Fremantle, called "Luminous Emptiness", that is excellent imo.

I think the "ancients" as you call them had a deep non conceptual understanding of death (and life), but the explanations are in another language couched in such different cultural terms that translators don't know how to accurately translate. Often they translate as if they are an authority, when they really are not. There is a LOT of knowledge out there that we haven't even begun to tap into, we are just fledglings, barely opening our eyes. We are very fortunate to have the opportunity have our scope onto "consciousness" (or whatever we're calling it at the moment) broadened a tad.

From what I understand on this topic, the ancient Egyptians utilized their lifetime and purpose for preparing themselves for the after-death experience, as well as a primary shift in consciousness.. such as expansion. I feel this is where most shamanism dwells, too.

From that, I feel it's important to learn from our history and implement various methods for preparing ourselves for that transition. We may never know truly what exactly it is, or what will happen, but it brings everlasting peace to those open and willing enough to explore our potential within these paradigms / realms of thought. And I think entheogens play an important role in that shift, as well as mindfulness / coherent thought. For balance of mind, heart and body gives way to furthering our inner being.

Bardo, bardo, bardo.
Right now is also bardo.


Of course, then there is the wonderful town of Bardo, Poland:

A life free of the anxiety of death sounds wonderful.