In sports, it's called being in the "zone" or the "flow". Performers, like athletes, who are in the zone, often speak of not "thinking" about what they're doing. They often describe a state of relaxation and focus, as if the performance is coming forth spontaneously from deep within, rather than forced. That ability to perform at the very highest possible level is possible in negotiation as well. Like athletes in the zone, good communicators don't seem to get thrown off by difficult issues or tactics or people.