Really great question! I've had a few occurrences where the experience itself compelled me to sing. Two of which, a being of pure rainbow light came to me in which i felt the most intense and wonderful feelings of ecstatic
love rushing through my body by just being in the presence of this entity. Both of these experiences, my eyes were completely open (physically and transcendentally). It was as if the songs were
pulled out of me in both reverence and a seeming resonance with the entity, that it was some sort of angel but at the same time, a higher version of myself. It was the same being both times, unmistakably.
Another experience, feeling the machinery of the universe and understanding myself to be a part of it, i had a complete understanding of what 'Krsna' means. I felt the sheer force of the divine impressed upon my consciousness, so much so, that i felt a tremendous amount of fear at what i was experiencing. In hindsight, it bore striking resemblance to the instance experienced by Arjuna when Krsna shows him his universal form in the Bhagavad-Gita, though at the time i did not make this distinction, yet found myself singing/chanting Hare Krsna as a sort of call for help until i came out of it.
There have been a few other times in which the compulsion to sing either to the entities present or to the universe itself; all of which, however, seemed to be flowing
through me in connection with the seemingly objective beings, as opposed to consciously making the effort to sing.
Ayahuasca on the other hand, is quite a different story.
ॐ असतो मा सद्गमय ।
तमसो मा ज्योतिर्गमय ।
मृत्योर्मा अमृतं गमय ।