Over seven years before his arrival on the island, Geoffrey suffered a breakdown on stage (the result of stress and betrayal and a mind that was probably just a little bit prone to this sort of thing anyway) and was institutionalised for about a year. For the past few months, ever since the death of his mentor (Oliver), he's been seeing and interacting with his "ghost", which is really just a product of his own mind though he's only just starting to come to terms with that.