It depends on what trauma a person has gone through. The age if the person at time of trauma and the length of time of traumatic experience.

We can only regress to the age of our emotional age at time of trauma.
Regression is an attempt to repair. Depth of dissociation depends on how much the person had to split.
Some just 'go away' for a few seconds, others like myself, completely numb out to protect against further splitting.