Is this a shared hallucination? Or has reality been warped forever?

In the Community, children and teenagers take a daily pill to develop their immunity to a hallucinogenic plague. Upon reaching adulthood, their immunity is tested. Those who fail the test are forced to leave their homes and sent to a remote facility for treatment, while those who pass join the hardworking ranks of society.
 
Reclusive high schooler, Erin, keeps to herself and a few close friends. She can’t risk exposing her secret: that she’s already experienced the plague’s symptoms.
 
But when the door to the nurse’s office vanishes and the halls shift, revealing a haunting treatment facility with monsters for patients, she’s not the only one who sees the monsters.
 
As Erin faces the unnerving possibility that everything she’s believed about the Community masks a terrible secret, she’s forced to decide which version is real.
 
She’ll have the choice to escape, but to where?