Oh, I thought it was so obvious. The show leads you to believe:
Survivors from a plane crash - caused by an escaped electromagnetic burst due to random numbers not being punched into a 1970's mainframe stemming from a 30 year old incident caused by an hbomb explosion they themselves set off - are miraculously healed on their new island home before being visited by ghostly apparitions of loved ones, attacked by an ethereal smoke creature, kidnapped and accosted by murdering indigenous others led by an ageless 400+ year old man, transported through time, escaping said island, returning to said island at the behest of battling demigods, watched the dead resurrect, and in the end saving the entire world by plugging up the egyptian hole in the glowing cave...
= REAL LIFE.
Plane passengers living out their daily, mundane lives in Los Angeles before experiencing bouts of weird deja vu and coincidental meetings...
= FAKE, constructed Limbo way station en route to eternal life
See how easy that is?