Thank you for clarifying a bit.
If I'm to be honest with you, I have no reliable basis to argue with you from, as I haven't found a reliable way nor a sound proof that I even exist (by "I", I mean to say as an individual, separate from other individuals - something obviously exists or there would be no experiencing), let alone what is true or not true about reality.
For instance, do I have freewill? It seems so, from my limited perception (conscious awareness), but it could be that everything I do and say is pre-determined or entirely outside of my control.
That being said, based on my own direct experiences, I agree to some extent what you have said about the human body being capable of achieving far more than the average person gives it credit. However, I don't think that it's sound reason to project that observation into meaning that anything is achievable by the human body, or by any type of meditative (transcendental) state of awareness. How could I ever know if, or where, my limits exist?
Also, I've never directly experienced, or had proven to me, the existence of immortality, so it's not a "truth" to me. Of course, the above doesn't prove that it doesn't exist. Again, I'm left back where I began, admitting that I don't really know anything.