The Ending - anyone read the book?

SPOILERS!

The credits show that this film was based on a book -- how did it describe the ending?

I've read a few threads here about the ending and there's a lot of talk of parallel universes. My first impression when I first saw this decades ago was (as I've seen mentioned here), "Oh, it looks like he swapped places with where all the other Earth inhabitants during the first event".

But on this viewing, I see no evidence of that on the beach he landed on. I mean, no hints there had been anybody else there prior.

However, I did notice a new thing. Earlier in the film when Joanne and Api are describing their near-deaths during the event, they described 'going towards the light' and the film gave us a red-colored visual of a tunnel. Of course, going to the light is a common near-death description (in real life, not the film).

After Zac presses the button on the explosives, but before he ends up on the beach, we see that same red tunnel. So are the film-makers placing him in some sort of afterlife? Is there a religious meaning to be had here? Or rather than "heaven", could they be saying that our after-death life-on-earth is just going to the next plane of existence? (Which could also fit in with the 'alternate universe' theory of the ending)?

And I wonder how the book describes that part. Anybody?