Somehow, I seem to be forming mandalas within my psyche without any particular knowledge of how I'm doing so. I'm merely walking around, or meditating, and there will occur mandalas of great complexity (usually of the same shape) which arise in my mind. When they do, my mind will explore and think about them, almost obsessively, and attempt to understand them. Any idea about this?
I've had similar experiences. Though Buddhism doesn't directly talk about the Kundalini system or even use the terminology (though Tibetan Vajrayana Buddhism has something close or maybe the same in Thummo), reading about it was useful from a systemic analysis perspective.
Regardless of any explanation I found, it was ultimately only for curiosity satisfaction.
I think the best approach is to continue to practice and to not get carried away by this. Especially not obsessively, as you state. Just observe, remain equanimous and go on about your meditation.
One could term it a nimitta in the Theravada tradition, I suppose.
In any case, it is a good sign of powerful concentration, keep at it.