This study shows links between Long COVID’s neurological effects, including brain fog and cognitive decline, and brain blood vessel integrity, offering hope for new treatments and diagnostic methods.
https://www.nature.com/articles/s41593-024-01576-9 (open access)
A sinus headache is distinguishable from a regular headache, so I wouldn’t discount the leaky blood vessels possibility.
Good point pointing out the difference between a “leak” and a “bleed,” though: if your brain is bleeding, that’s a full-blown emergency.