I fearlessly predict the advent of a new psychological problem. It will show up within twenty years, I think, and you'll soon understand why it has never been seen before. The problem is that a few people will get quite upset, perhaps unable to function at all, when they can be fairly certain there is no one they know within, say, twenty miles of them. In the converse illness, people will be unable to function when, say 2,000 or more of their friends and acquaintancecs are within a few hundred feet.
In order to facilitate these illnesses, we need a few technological advances that are just now on the horizon. With the ability to locate people accurately, check them against databases of friend-relationships, and download statistics about who's nearby to PDAs, it will become possible to warn people when their dread condition occurs. And don't think they won't want to know about it!