Two sisters on Mexican vacation are trapped in a shark observation cage at the bottom of the ocean, with oxygen running low and great whites circling nearby, they have less than an hour of air left to figure out how to get to the surface.
This movie contains 23 potentially triggering events.
Spoilers: towards the end of the movie, one character starts suffering from nitrogen narcosis and hallucinates. You can't tell what's real for a little while.
SPOILERS
one of the sisters is dragged away by a shark and although in a hallucination she lives the reality is that she is still gone but it doesn't clarify whether she's dead or not