Requiem
(2006)

After suffering her entire life with epilepsy, Michaela Klingler (Sandra Hüller) becomes convinced that her seizures are really due to demonic possession. Though they initially reject her claims, she manages to convince nearly everyone around her that an exorcism is what she truly needs.

The film ends with her best friend making one last attempt to persuade Michaela to go to the hospital and seek medical help. Michaela is certain that this is the path God has chosen for her, and that her suffering is for a higher purpose. 

An epilogue states that after several dozen exorcisms, Michaela Klingler died of exhaustion at her family’s home.

Thanks Melodylyn!