I'm thinking that what with the information that several of our Oceanic 6 members are being haunted/visited by their deceased loved ones (Hurley/Charlie, Jack/Christian) emploring them to 'go back to the island', it now makes sense that Jack wasn't being
sarcastic nor is Christian still alive in 3.23 (Through the Looking Glass)..but that Jack was being
haunted by his father (or a manifestation of..). Perhaps on a nightly/daily basis, to the extent that it ultimately drives him over the edge. So much so that he literally tells doctor Hamil that his father is upstairs. He is..just in 'ghost/spirit' form..
