This is an interesting observation.

A simple explanation could be:
Jack talking about his dad is partly because of Jacks drug use, partly Jack's depression, and mostly the writers tricking us in to thinking it was a flashback.

Hurley has a history of seeing people that aren't there and having physical interactions with them. (if I remember right Dave threw something at Hurley and it hit him in the stomach. kinda like Charlies slap.)
The real interesting thing with Charlie's visit was that another patient saw him too.

And agree with what you said about Sun being under stress while giving birth.

I don't see what more it could mean. But I think there is more to it. And it will probably continue to be a theme as we see new flashforwards.

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Doctor playing golf. Woo, boy howdy, now I've heard everything. What's next, cop eating a donut?