A 10-year-old girl is brought to the emergency department about 30 minutes after waking up and discovering that she had completely lost vision in both eyes. Her vision was normal when she went to sleep around 10 hours ago. She is conscious and rational at presentation, but then abruptly develops a tonic-clonic seizure that lasts for about 2 minutes and terminates spontaneously. This is her first such episode. She has had a generalized severe headache for 1 day and low-grade fever for 4 days. These were treated with over-the-counter acetaminophen (paracetamol), at an age-appropriate dose. Her parents did not seek medical attention. Her medical, surgical, family, and birth histories are unremarkable. She is not on any routine medications. There is no history of allergies. A complete blood count and liver profile are within normal parameters.