Unprepared is the word many use when they suddenly realize they are lonely. This often occurs to people settling into a new job after moving away from their home. They may feel there is no one in the world to care about them or be with them. The world seems to be a hostile place where they must fight to even survive. This is fairly common when a person is beginning to make the adjustment to a new life. It is not pleasant, but it can be endured and cured over time.
Being in a new culture or location is unsettling. This is true even if the person requested the transfer or went after the job because it entailed world travel. When they realize they are lonely, they need to get out and explore their new world. It will take time, but eventually they will find a way to adapt to their new home. They will meet people and build new friendships. It just takes a bit of time and effort on their part.