...WOKE UP AND IT WAS ALL A DREAM.

I don't care how contrived the explanations are as long as they aren't that, really. Jack's dad - I think maybe he had a weird connection to the island which caused him to turn to drink for escapism. Or people just keep on seeing things they saw off the islands. Like Kate's horse etc...

There's a good chance Hurley had seen Christian Shephard before, everyone keeps on popping up in one another's flashbacks.