Meditation Darkness

I'm puzzled these days about how to tell whether a particular mind-state that I experience in meditation is something to explore or merely something to note when it arises, and then to return to the breath.

This morning, meditation began as it usually does -- several minutes of settling in, a few minutes of concentration on breath, and then the process of watching thoughts arise and subside. Then a small mind-shift occurred, and the mind-experience changed to a kind of darkness -- like being suspended in thick, black, velvety air. As an external sound would occur, there would be a mind-shift back to note the sound and the body state, all the while the mind continued to experience the black velvety air, but to perceive it more dimly. Then the mind moved back into that experience, and the external world subsided. Then the mind recalled the Yoga Sutra instruction of pratyahara (withdrawal of senses), and that brought the attention from the darkness back to the memory/mind. Then the mind moved back, a little ways, into the experience, and finally the meditation ended.

It would be interesting to know of others' experiences with such occurrences.