The characters in the movie have played so many ultra-real games they can no longer tell when they are in reality.
Red pill or blue pill?
then you go offline and deal with meatworld, where you're likely to say Weren't you listening? Scroll up!
Existenz is, in my humble opinion, better than The Matrix in terms of alternate realities. Matrix started out OK, especially if you've read “I Have No Mouth But I Must Scream” but then turned into Crouching Tiger-Hidden Dragon only with guns.
I had to watch Existenz twice to figure it out. The little three-headed mutant amphibian (at the gas station where they are being fitted with spinal data implants)is a clue. Gibson meets Phillip Dick in a dreamworld sort of thing.