The phenomenon of seeing people you know/knew when they aren't really there. Happens in streets, stores, parties, airports; makes you turn your head and realize what your reaction would have been if they were there. Maybe it is this face in a crowd, or familiar stoop walking out the door. Maybe it is totally manufactured, but you just want to believe.
Indications:May cause intense longing. May cause belief that there are only just so many people in the world, and they occasionally wear disguises. May cause disorientation; please abstain from seeing ghosts while driving. May cause high phone bills: please be warned.