A 46-year-old woman presents about 20 minutes following a generalized tonic-clonic convulsion, which was witnessed by her husband and lasted for 5 minutes before subsiding spontaneously.

She was drowsy and confused in the first few minutes following the convulsion, but recovered completely afterwards.

She has had diarrhea, sweating, palpitations, and difficulty sleeping for the past two days, and a cough and a runny nose for the past week.

Over the last three months, she has lost 5kg of weight and has experienced intermittent palpitations. There is no history of headaches, photophobia, or neck pain.

Her further history is unremarkable. An urgent electrocardiogram (ECG) is only significant for sinus tachycardia, with a rate of 118 bpm.