Actually, it’s very rare for ghost-types to possess people. It only really happens if the human invites a ghost to do so. (This is why channelers and hex maniacs tend to be more susceptible to it: they’re often working with ghosts to the point where they run at a risk of accidentally inviting such behavior.)
More often than naught, though, hex maniacs are simply eccentric people who are very fond of white contacts, not victims of possession. The behavior you’ve just described, for example, actually sounds pretty accurate for the average hex maniac.