You are unable to do both at the same time. In doing the TET, we notice the discrete segments of independent footage that are presented with a rapid-fire quality. We methodically weave them all together into a coherent narrative. Our actively synthesizing mind, our labor, goes on while we sit back, relax and absorb. It would seem that our minds are in high gear without our knowing.
Relaxation implies renewal.
One runs hard, then rests. While resting the muscles first experience calm and then, as new oxygen enters them, renewal. Images are pouring into it. Your mind is not quiet or calm or empty. It may be nearer to dead, or zombie-ized.