Naad, which is a sanskrit word which when transalted into english language would be "Numen", as this numen is a thing which is happening at all the times within the body by the life energies which are continually moving within, their movement is not random but is in a prescribed manner in synchronization with the energies nearby, around them and also with the energies which arent nearby or around them ( this can be better understood as to the huge mood swings which person experiences when there is full moon or no moon day, or when the person is close to a natural water body, like lake, river or ocean) . The ethos of the movement of the energy is based upon charge and polarity these life energies also have their movement based upon the charge, and within the body the movement of these emergies can be broken down into three phases
Recieving
Assimilation
Transmission
the polarity of the transmitting organ and the polarity of the recieving organ their behaviour in respect to each other, defines the speed and the smooth transition of the energy, and during each of these three phases and 81 sub phases, a Naad is produced, this Naad is not produced due to collision of the energized ions but due to their movement in relation to the ions of contrasting polarity and charge.
When these ions are substantiating each other and assisting in the movement as so for gaining higher charge the person is better placed to realise the correlation of the life energies with the cosmic energy and such a person is popularly known as realized master, but this is not as easy to achieve as it is to read, as there are lots of things which that person needs to refrain from which are taken as normal in the present soceity and living, hence the life of that person and the control over its life is better than the rest, kind of food and moral conduct are just two of many principles.
The innuendo of Naad yog are also derived from these very principles, the logics of energy, the primal rule of energy, it comes from nothing forms something and then again goes to nothing, as what is even enshrined in the vedas long before the present science could prove,
ना तत्समय ना प्रतिमा अस्तेय शिवम
The principles of healing by Naad yog are planked upon these facets itself, there is discrepancy in the movement of the energy and/or its synchronization with the other invisible energies. As by Saadhna/deep dligient practice of Naad yog it is "Known" to the author (it is known by experience and learnt by reading someone else's experience) that any discrepancy doesn't happens due to one kind of energy but there are two or more energy forms which are negatively effected and this effect is the cause for any and all phsyical, mental, emotional psychological illnesses.
The reasons for illnesses is due to imbalance or random behavior of the energies, which hence can be because of so many reasons, that's why appropriate evaluation of the astrological chart is necessary, it is only post the evaluation of the astrological chart that any healing shall be initiated, as there can be some other reasons for illnesses apart from just a disorder.