my dissociation in public was a bit different than what you describe. you see here in my location its not called dissociation when someone has an internal imaginary world or imaginary place. here in my location thats now called day dreaming, using ones imagination, imaginary play, and depending upon how much it affects a persons life my location also calls it autism, Schizophrenia, psychosis, delusions, depression and many other mental illness issues depending upon what is causing a person to clip into or choose to live in their mental worlds instead of reality.

my dissociating in public were things like if I got stressed out, anxious or otherwise triggered I would have dissociative symptoms (numbness, foggy minded/spacey\spaced out, disconnected (feeling of unrealness of my limbs or those around me but knowing they were real)

the key to fixing this problem for me waa to get physical, if I was feeling dissociated sitting at my desk I would stand up and stretch or go to the coffee machine for a fresh mug of coffee, if I felt dissociated at home and it was nice out I would go down to the lake and row my canoe around the lake getting back in touch with my surroundings.

my suggestion if your entering your mental world continues to bother you contact your treatment provider, maybe even print off your post so that they can read what its like for you so that they can diagnose and treat you for this problem.