We do not currently know of any antonyms for anatomical position.
The noun anatomical position is defined as:
The position of the human body, standing erect, with the face directed anteriorly, the upper limbs at the sides and the palms turned anteriorly (supinated), and the feet pointed anteriorly; used as the position of reference in description of site or direction of various structures or parts as established in official anatomical nomenclature. Note: The palms are toward our view and we cannot see the back of the hands.