A 22-year-old female with no prior psychiatric history is brought to the psychiatric emergency department after 3 weeks of progressive behavioral changes. Her roommate reports that she initially became anxious and irritable, then developed paranoid delusions and auditory hallucinations over the following days. In the past week, she has had two witnessed generalized tonic-clonic seizures, episodes of facial dyskinesias with lip smacking and jaw movements, and periods of decreased responsiveness alternating with agitation. On examination, she is disoriented, exhibits orofacial dyskinesias, and has autonomic instability with fluctuating heart rate and blood pressure. A CT head is unremarkable. Basic metabolic panel, liver function tests, and thyroid studies are within normal limits. CSF analysis shows mild lymphocytic pleocytosis. Which of the following is the most likely diagnosis?