A 57-year-old man presents with a retro-orbital headache for three days. The headache was sudden in onset, and has been persistent and severe, with no response to over-the-counter analgesics.

Despite this, he refused to seek medical attention until earlier today, when his family members became highly concerned as he was acting confused, and claimed that 'he couldn't see clearly'.

There is no history of severe or recurrent headaches in the past, or of any recent trauma. His medical history is only positive for mild hypercholesterolemia which is well controlled on diet alone. His surgical and family histories are unremarkable.

A complete blood count, renal and liver profiles, and clotting screen are performed. The only significant finding is a serum sodium level of 117 mEq/l (normal: 135-145).