From Sakyong Mipham's Running with the Mind of Meditation, Chapter 31:

The level of clarity that occurs during meditation is not simply the result of physical activity. Rather, clarity is what the mind is, like the sky. Stress and agitation are like clouds. If we don't see the sky very often and it suddenly breaks through the clouds, its clarity may feel like an anomaly, but we know it is the sky. Just so, when the practice of meditation lets the natural skylike mind break through the clouds of discursive thought and worry, what we are seeing is the mind's innate clarity, awareness, and joy.

^z - 2015-02-15