I struggle with this sometimes. My T says its dissociating. A self protection tool I learned from trauma.
Grounding techniques usually can help me get back to the present... the here and now. If I am alone I will speak certain things out loud, but when I with others I say it in my head.. examples: saying what day it is, month, year.. try to find/name 3 things in the room that are a certain color, or begin with the same letter..... tapping my feet on the floor also helps me... and there are many breathing exercises just like you can use when having anxiety or panic attack. Sometimes, leaving the room, excusing yourself... like need the bathroom is one of the most useful tool.
I also deal with auditory hallucinations ... but to me, at least, the feeling you are describing is a different thing.
I hope that helps.