Isolation Dynamics and the Impact on Relationships: Perspectives from Within

What is the inner experience during phases of fragmentation or detachment that lead an individual to shut down within a couple relationship?

For those who directly experience this condition: does the sudden withdrawal from the emotional bond represent a protective response, a profound energy depletion, or a component of temporary disconnection? What dynamics arise in the perception of the partner, and what actually happens on an emotional level when this wall is built?

Any contribution based on direct experience is helpful in understanding the true dynamics of the disorder within a shared life.