I have very similar experiences from partnered improvized dancing, my main style being the Argentine tango. For at least last 10 years, my aim has been to find obstacles that prevent me from experiencing such a state, and experiencing such a state has become more common.
I have used almost the same words to describe my experience: although I am the leader in the couple, and everything is improvized to the music, I feel like I am the spectator, and I feel the couple is moving like a single animal, one head and four legs.
I have used almost the same words to describe my experience: although I am the leader in the couple, and everything is improvized to the music, I feel like I am the spectator, and I feel the couple is moving like a single animal, one head and four legs.