About the only thing I can come up with is that your energy body was stretching, going along with your attention. I've had a 'balloon inflated' feeling before, but no skin stretching.
Inducing 'vibes'!!! That is Awesome. That has been very much my goal for many years. Good on ya! For me, the vibrations are usually joined by paralysis. (not always, but usually.) There is also a very strong, full body, steady, HUMM that is aslo seperate from the 'vibes' and the paralysis. Seperate energy-body sensations/effects, but usually occuring at the same time as the 'exit'. Of course there are other 'exit' phenomenon too. I have limited or no luck producing exit sensations at will. I can move energy quite easily (mostly), and practice daily energy work, but the act of producing vibrations at will has always eluded me.