Medical science is conducting trials on a process that is attempting to bring the dead back to life. It is quickly replacing a person's blood with cold saline solution to create a suspended animation where the brain and other organs shut down but do not die. This gives physicians time to repair damaged organs and revive the patient.
Science fiction has its share of bringing back souls from mummies to vampires to Dr. Frankenstein.
In LOST, one of the open questions is still whether the main characters were "alive" or "dead" on the island. One group believes they died in the plane crash and the island was their purgatory. Another group believes they survived the plane crash and were human survivors on a mysterious island.
But what if we twist those beliefs.
The theory is that the main characters were dead souls in the sideways world, but they were brought back to life on the island world in order to work out their past life's issues.
It is a handy theory because it in some ways neutralizes the "are they alive or dead?" debate with a unique premise that the characters were both dead and alive.
The "reincarnation" takes place in the after life when the souls take "a plane ride" to LA, but are split into a new body as an island survivor. As a survivor with no memory that they are already dead, continues to live out their lives through their memories, which are reinforced by the island's supernatural smoke monster. The island is a form of group therapy for troubled souls who have regrets that hold them back from moving on in the after life.