In one commentary called The Wheel that Outlines the View of the Cuckoo (khu byug gi lta ba gcod (spyod) pa'i 'khor lo bzhugs, Bairo rgyud 'bum, nga, ppg. 341-351), at the beginning of the commentary we find an interesting explanation of the name of the text for the best type of student. Within this section, there is an explanation through a simile for the word "cuckoo" in the title of the rig pa khu byug:
For example, just as when the physician, Jivaka Kumara touches the inner pulse, to begin with, he knows as soon as the illness attacks, and where the illnesses is at present, and what to do; the person of best or medium faculties knows, to begin with, that the basis divided into samsara and nirvana though it is single, how there is the fetter of both concepts at present, and how there will be liberation after turning back in the end.
This metaphor and its meaning presents a whole host of interesting resonating metaphors going back to the Buddha as a great physician. Closer to home however, is the imagery of the separation of samsara and nirvana as a key feature of the Tibetan medicinal system. This concept finds another expression in a text in the Eighteen Sections (cha lag cho brgyad, Beijing, 2005, a group of important texts that preserve writings by Yuthog the younger and his immediate disciples, Ye shes bzung, and so on), the seminal The Historical Outline, the Soaring Great Eagle (khog dbug khyung chen lding ba, ppg. 4-5):
...long ago when Buddhas had not developed, and also sentient beings had not become deluded, since the empty mind which had formed spontaneously without depending on any cause, was not established as a thing or a characteristic. Since knowing (rig pa) appeared without ceasing it was not threatened with murder or interruption by any remedy, did not fall into one-sidedness, having always existed from time without beginning. The meaning of that is that dharmakaya Samtabhadra is designated from basis' original self-recognition and liberation i.e. omniscient in all respects, buddhahood. The mind was empty and without activity for a long time, and because of being subtle and hard to identify, it did not recognize itself and wind piled up on its own wind, and light illuminated itself with light, and since it was not able to remain within its own location, the sentient beings of three realms arose from delusion and wandered in samsara.
Here we have an expression of the basic difference between health as Buddhahood and illness as the state of being a sentient being. The explanatory tantra states:
There is a single cause of all disease i.e. called ‘ignorance’ because of not understanding the meaning of absence of identity.
The state of health in Tibetan medicine is termed "unaltered" (rnam par mi gyur, avikrita), the state of unhealth is termed "altered" (rnam par rgyur, vikrita). When we discuss the simile of the three roots of the mnemonic tree of Tibetan medicine, the first root is gnas lugs, or state of existence, being one root that has two trunks, unaltered or healthy; and altered, or unhealthy. So as in the khu byug commentary, health and unhealth are shown as polar choices on the basis of a single thing that is either affected or not affected by the knowledge obscuration of ignorance.
The metaphor here can drawn out further, for just as we are generally unaware of our bodies until they become ill, likewise, we are generally unaware of the separation of the states of samsara and nirvana until we suffer. Likewise, we need a diagnosis to understand this condition, and further we need to do something i.e. use a treatment, we need to know what to do so that we can return in the end to that state of health. And finally, the metaphor is tied up with the fact that the basis is the mind, which is either in a state of knowledge or delusion. Likewise, the body, being the gross expression of the ripening of the actions instigated by the mind, is in a state of health or illness depending on the three humors that ultimately arise from the knowledge obscuration of ignorance.