Returning to my country of birth after living overseas for 3 years, I found I had absorbed the customs and greetings of my host country, words automatically came out of my mouth wrong, and my brain couldn't switch back without even realizing, walking around the supermarket in my home country felt surreal and weird. Full reintegration took about a year. In my opinion, don't underestimate how as humans we adapt and meld into our surroundings without even being aware of it. Be patient with ourselves - it takes time