Your target must succeed at a Will save or believe it can no longer breathe. An affected target must attempt a Fortitude save each round at the beginning of its turn. The first time it fails the Fortitude save, it is staggered until the next time it attempts a save against the spell. If the target fails a second Fortitude save in a row, it falls unconscious for the spell’s remaining duration. The target breathes normally while unconscious, but is shaken for 1 minute upon awakening. If the target succeeds at two Fortitude saves in a row, it shakes off the spell’s effects entirely. Otherwise, the target continues to attempt a save each round until it falls unconscious or the spell ends. This spell has no effect on creatures that don’t need to breathe.
Pathfinder Roleplaying Game Horror Adventures © 2016, Paizo Inc.; Authors: John Bennett, Clinton J. Boomer, Logan Bonner, Robert Brookes, Jason Bulmahn, Ross Byers, Jim Groves, Steven Helt, Thurston Hillman, Eric Hindley, Brandon Hodge, Mikko Kallio, Jason Nelson, Tom Phillips, Stephen Radney-MacFarland, Alistair Rigg, Alex Riggs, David N. Ross, F. Wesley Schneider, David Schwartz, Mark Seifter, and Linda Zayas-Palmer.