A question about the final episode of Lost, Season 3...? (Spoilers!)?

So in the final episode, we realize in the end that the story about Jack being a "hero" was a flashforward, not a flashback. But...what about the scene when he's arguing with that doctor who accuses him of being drunk and Jack says, "Call my dad from upstairs and we'll see which one of us is more drunk." Huh? Is Jack's dad really dead? Was this really not a flashforward like we thought it was? Or just a mistake?

That's right...I forgot that his dad's coffin was empty!!! Damn, why do I have this stuff on DVD if I don't watch AND remember it???

I noticed that he referred to his father being alive, not only then, but one other time, and no one corrected his statement.

so my guess is that who ever was in the coffin that he put on the plane was not in fact his father, factor in 'Dad's' disheveled look in the Ana Lucia, and Sawyer flashbacks, its possible that Jack claimed another Drunk, and his real dad got clean and returned home when he saw news of his son and Flight 815 going down.

considering the context in which he cited his dad I doubt he was referencing heaven when he said 'upstairs'

mmm, i see where your going with this...great question.

I'm sure it wasn't a mistake, but I don't know what it means. "Upstairs" could be a reference to heaven, or it could be something else. Remember, the coffin was empty...

I personally think this was done for two reasons:
1) To enforce the perception of it being a flashback to the viewer.
2) To show Jack's mental instability.
It was definitely a flashforward (the first of many to come) and definitely wasn't a mistake. Nothing in Lost is done by mistake!