A 40 year old female presents with a history of sudden onset of headache and nausea which passed off with rest and analgesics.Later she developed blurring of vision for a few days. On the day of admission she had developed third nerve palsy with neck rigidity. The temperature was 100°F.The most likely diagnosis is -
Acute attack of migraine
Viral encephalitis
Sub-arachnoid haemorrhage
Severe hypertension