”Those who are expert in yoga science say that feeling lightness in the body, disease free in every way, detached from material sense objects, having luminous complexion in the body, a sweet sounding voice, pleasant odor in the body, and reduction of evacuation, and urination are the preliminary external signs (symptoms) of perfection in yoga.”
laghutvam arogyam alolupatvam
varna prasadam svara-sausthavam ca
gandhah subho multra-purisam alpam
yoga-pravrttim prathamam vadanti
PURPORT BY SRI KRSNA BALARAM SWAMIJI
Besides having spiritual powers to control the material elements as stated in the previous verse a yogi obtains internal powers as well. His body becomes so light that if placed on water it will not sink but float like a boat. He always remains free from diseases. It does not matter what he does, diseases do not touch his body. Material things seem to him no better than garbage. As Chanakya Niti states, para-dravyesu lostavat.
“He sees other’s valuables equal to mud.” If he sees sense objects he does not feel attracted to them. He physically becomes very attractive. Without using any fragrant ointment his body releases a natural perfume like smell. His going to the toilet becomes reduced because his hunger becomes so reduced that consumption of food becomes practically nil. Such are his natural personal habits which great sages prescribe as preliminary signs of a perfect yogi.
[Svetasvatara Upanisad, 2.11, KBS0018]