I've felt a similar feeling when deep in thought before bed. I start to discuss what things mean on a deeper level with my inner self and then occasionally I start to feel like my whole body is heavier and rotating in a circle, like a spiral or some sort. I can feel this inner heaviness as it spins, it is a very odd sensation.

The insight that I have is when you feel yourself spinning its like shifting through a deeper part of yourself.

It could be that at a deeper level, we, the ones who have this sensation, in a peculiar way have insight when we meditate or even if we just alleviate, are becoming in-tune with our inner-self, and in that sense a level of spirituality that is separate from our biological form.

Just an idea.