I remember a client I worked with years ago who had very little awareness of what was happening inside his body—or even where his body was in space.
In other words, both his interoception and proprioception were limited.
At one point, I gave him a very simple exercise: lie on the floor with his arms out to his sides.
I demonstrated it several times. I explained verbally—and even in writing—that the purpose was to gently create length across his chest, allow more freedom in his breathing, and encourage external rotation at the shoulder joints.
And still, the exercise remained somewhat mysterious to him.
At the time, I didn't understand something I understand much better now:
I was asking him to notice sensations he may not have learned how to notice. I was giving him the exercise, but I wasn't helping him develop the internal awareness that would allow him to experience the exercise differently. This internal awareness is the powerful and often overlooked interoception. 

What Is Interoceptio...