When intracranial pressure suddenly builds, the brainstem can be compressed and pushed through the magnum foramen, cutting off oxygen and circulation to the brain. Symptoms include unilateral fixed and dilated pupil, coma, posturing, hypertension, and respiratory arrest. Systemic sepsis and allergic reactions are likely given the patient’s symptoms. Brain infarct may lead to intracranial hemorrhage in rare cases, but these brainstem herniation best accounts for these symptoms.