Is/are there any medical explanation(s) for the vibrational stage preceding astral projection?

Fantasy

Mechanical oscillations above an equilibrium point

They would need to know at least what is vibrating, and preferably at what frequency, and with what wave-form. If someone can provide that information, I’m sure they will get right on it. Trying to apply the scientific method without data is as fraught with peril as playing leap-frog in a nudist colony.