When pursuing your Minds true nature, what you review as precious experience born out of decades of trial and error, is all but an illusion.
Unborn Mind, primordial Mind, uncreated Mind, your true nature, cannot be bargained with, pleaded with, tricked or otherwise made to show itself to something impure, because the latter is what your Spirit imagines itself by eons of errors to be, which is something empty of truth and hence out of phase with truth absolute, which your Unborn Mind is.
In order to behold your true nature , your Spirit, i.e. your pure will, must remain as such, that is, perfectly undivided as one and not two or more, thus pure and not holding on to the slightest thought or thing or emotion nor memory and expose itself solely to its own Unborn Mind – there before all things and all creations – as their Master and Lord. In the beginning this takes great effort, because there is resistance from the demons within the student that have grown from tiny seeds somewhere long ago to great ghouls of influence in the student’s mind. There are two ways to fight them; either one by one (Theravada), which takes time, or all at once in one swift cut with Manjusri´s sword (Zen), which is instantaneous. To each their own choice; although the latter is advised and preferred by students of good merit and virtue.
Can this be achieved by sitting, walking, or lying down? If you believe in any of these positions you have yet tried to gain an advantage through a fixed position over something position-less, imageless and impervious to all attempts of worldly entrances.
To be One with this One Mind, your own mind must be completely unbiased, undivided and hence pure (holding on to no image whatsoever). Not even this body of old karma you are dragging around day and night looking for the jewel brighter than all dharmas it reflects in the essence of its own luminous body.If you can focus the will of your entire being on this for even a split second, then you will break through the wall of the evil skandhas and attain Satori, which is produced by an awesome light that naturally leads to the noble wisdom (prajna).
This wisdom, one not born out from anything of this world or other, empowers and enables you to distinguish between the true and the false in any given place or age. Hence you are liberated, free from any further suffering born out of ignorance and error, and can remain an unconcerned being the remainder of your worldly presence in this world system, all in accordance, if desired, with your residual karma.