Perhaps a CSF leak due to a dural sack tear in the spine? Was his symptom only having headaches while standing? Happened to my wife. 6 weeks of absolute hell.
On second thought — the opposite. A bulge/blockage of CSF?
Apparently, as I've recently learned due to a debilitating headache, CSF pressure (both high and low) can cause a whole host of symptoms, ranging from mild headache and blurred vision to coma and death.
It's pretty wild that a doctor wouldn't have that as a hypothesis.
On second thought — the opposite. A bulge/blockage of CSF?