Culture shock refers to the anxiety and feelings (of surprise, disorientation, uncertainty, confusion, etc.) felt when people have to operate within a different and unknown cultural or social environment after leaving everything familiar behind and they have to find their way in a new culture that has a different way of life and a different mindset.
Good post by Jan Chipchase on When Professionals Get Culture Shock.
And remeber, there is also the reverse culture shock:
Also, Reverse Culture Shock (a.k.a. Re-entry Shock, or own culture shock) may take place — returning to one’s home culture after growing accustomed to a new one can produce the same effects as described above. This results from the psychosomatic and psychological consequences of the readjustment process to the primary culture. The affected person often finds this more surprising and difficult to deal with than the original culture shock.