I try not to dwell on it.

Think of it like a sixth sense, an extension of yourself. It operates on a secondary… hm… I guess frequency? Than your physical body. If you use too much of it, you’ll get dizzy and exhausted like you’ve just run for too long, but it won’t last very long. I guess you could say a unicorn recovers faster from spellcasting than physical activity. It’s why a lot of us use it so much.

To more directly address your question, it just sort of feels like bending your knee, or turning your head. It’s like a muscle.